GIFT   OF 
MICHAEL  REESE 


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OF 

UNIVERSITY 


THE  FILTRATION 


OF 


PUBLIC  WATER-SUPPLIES 


BY 

ALLEN    HAZEN, 


ASSOCIATE    MEMBER    OF   THE    AMERICAN    SOCIETY    OF  CIVIL   ENGINEERS,    MEMBER   OF   THE    BOSTON 
SOCIETY    OF    CIVIL    ENGINEERS,    THE    AMERICAN    WATER-WORKS   ASSOCIATION,    THE 
NBW    ENGLAND    WATER-WORKS    ASSOCIATION,   THE    AMERICAN    CHEMICAL 
SOCIETY,    THE    AMERICAN    PUBLIC   HEALTH    ASSOCIATION,  ETC. 


THIRD    EDITION,    REVISED    AND   ENLARGED, 
FIRST    THOUSAND. 


NEW  YORK : 

JOHN    WILEY    &    SONS. 

LONDON:    CHAPMAN    &    HALL,    LIMITED. 

JQOO. 


Copyright,  1900, 
BY 
.HAZjEN. 


ROBERT   DRUMMOND,    ELECTROTYPER    AND    PRINTER,    NEW   YORK. 


PREFACE  TO  FIRST   EDITION. 


THE  subject  of  water-filtration  is  commencing  to  receive  a 
great  deal  of  attention  in  the  United  States.  The  more  densely 
populated  European  countries  were  forced  to  adopt  filtration 
many  years  ago,  to  prevent  the  evils  arising  from  the  unavoidable 
contaminations  of  the  rivers  and  lakes  which  were  the  only  avail- 
able sources  for  their  public  water-supplies ;  and  it  has  been 
found  to  answer  its  purpose  so  well  that  at  the  present  time  cities 
in  Europe  nearly  if  not  quite  equal  in  population  to  all  the  cities 
of  the  United  States  are  supplied  with  filtered  water. 

Many  years  ago,  when  the  whole  subject  of  water-supply  was 
still  comparatively  new  in  this  country,  filtration  was  considered  as 
a  means  for  rendering  the  waters  of  our  rivers  suitable  for  the  pur- 
pose of  domestic  water-supply.  St.  Louis  investigated  this  subject 
in  1866,  and  the  engineer  of  the  St.  Louis  Water  Board,  the  late 
Mr.  J.  P.  Kirkwood,  made  an  investigation  and  report  upon  Euro- 
pean methods  of  filtration  which  was  published  in  1869,  and  was 
such  a  model  of  full  and  accurate  statement  combined  with 
clearly-drawn  conclusions  that,  up  to  the  present  time,  it  has  re- 
mained the  only  treatise  upon  the  subject  in  English,  notwith- 
standing the  great  advances  which  have  been  made,  particularly 
in  the  last  ten  years,  with  the  aid  of  knowledge  of  the  bacteria 
and  the  germs  of  certain  diseases  in  water. 

Unfortunately  the  interest  in  the  subject  was  not  maintained 
in  America,  but  was  allowed  to  lag  for  many  years ;  it  was 
cheaper  to  use  the  water  in  its  raw  state  than  it  was  to  purify  it; 
the  people  became  indifferent  to  the  danger  of  such  use,  and 


82943 


i  V  PREFA  CE. 

the  disastrous  epidemics  of  cholera  and  typhoid  fever,  as  well  as 
of  minor  diseases,  which  so  often  resulted  from  the  use  of  pol- 
luted water,  were  attributed  to  other  causes.  With  increasing 
study  and  diffusion  of  knowledge  the  relations  of  water  and  dis- 
ease are  becoming  better  known,  and  the  present  state  of  things 
will  not  be  allowed  to  continue ;  indeed  at  present  there  is  in- 
quiry at  every  hand  as  to  the  methods  of  improving  waters. 

The  one  unfortunate  feature  is  the  question  of  cost.  Not 
that  the  cost  of  filtration  is  excessive  or  beyond  the  means  of 
American  communities  ;  in  point  of  fact,  exactly  the  reverse  is 
the  case ;  but  we  have  been  so  long  accustomed  to  obtain  drink- 
ing-water without  expense  other  than  pumping  that  any  cost 
tending  to  improved  quality  seems  excessive,  thus  affording  a 
chance  for  the  installation  of  inferior  filters,  which  by  failing  to 
produce  the  promised  results  tend  to  bring  the  whole  process 
into  disrepute,  since  few  people  can  distinguish  between  an  ade- 
quate filtration  and  a  poor  substitute  for  it.  It  is  undoubtedly 
true  that  improvements  are  made,  and  will  continue  to  be  made, 
in  processes  of  filtration ;  so  it  will  often  be  possible  to  reduce  the 
expense  of  the  process  without  decreasing  the  efficiency,  but 
great  care  must  be  exercised  in  such  cases  to  maintain  the  con- 
ditions really  essential  to  success. 

In  the  present  volume  I  have  endeavored  to  explain  briefly 
the  nature  of  filtration  and  the  conditions  which,  in  half  a  cen- 
tury of  European  practice,  have  been  found  essential  for  success- 
ful practice,  with  a  view  of  stimulating  interest  in  the  subject, 
and  of  preventing  the  unfortunate  and  disappointing  results 
which  so  easily  result  from  the  construction  of  inferior  filters. 
The  economies  which  may  possibly  result  by  the  use  of  an  infe- 
rior filtration  are  comparatively  small,  and  it  is  believed  that  in 
those  American  cities  where  filtration  is  necessary  or  desirable  it 
will  be  found  best  in  every  case  to  furnish  filters  of  the  best 
construction,  fully  able  to  do  what  is  required  of  them  with  ease 
and  certainty. 


PREFACE  TO  THIRD  EDITION. 


THERE  have  been  several  distinct  epochs  in  the  development 
of  water  purification  in  the  United  States.  The  first  may  be  said 
to  date  from  Kirkwood's  report  on  the  "  Filtration  of  River 
Waters,"  and  the  second  from  the  inauguration  of  the  Lawrence 
Experiment  Station  by  the  Massachusetts  State  Board  of  Health, 
and  the  construction  of  the  Lawrence  city  filter,  with  the  demon- 
stration of  the  wonderful  biological  action  of  filters  upon  highly 
polluted  waters. 

The  third  epoch  is  marked  by  the  experiments  at  Louisville, 
Pittsburg  and  Cincinnati,  which  have  greatly  increased  our  knowl- 
edge of  the  treatment  of  waters  containing  enormous  quantities  of 
suspended  matter,  and  have  reduced  to  something  like  order  the 
previously  existing  confused  mass  of  data  regarding  coagulation 
and  rapid  filtration. 

The  first  edition  of  this  book  represented  the  earlier  epochs 
before  the  opening  of  the  third.  In  the  five  years  since  it  was 
written,  progress  in  the  art  of  water  purification  has  been  rapid 
and  substantial.  No  apology  is  needed  for  the  very  complete 
revision  required  to  treat  these  newly  investigated  subjects  as  fully 
as  were  other  matters  in  the  earlier  editions. 

In  the  present  edition  the  first  seven  chapters  remain  with  but 
few  additions.  Experience  has  strengthened  the  propositions 
contained  in  them.  New  data  might  have  been  added,  but  in 
few  cases  would  the  conclusions  have  been  altered.  The  remain- 


VI  PREFACE. 

ing  chapters  of  the  book  have  been  entirely  rewritten  and 
enlarged  to  represent  the  added  information  now  available,  so 
that  the  present  edition  is  nearly  twice  as  large  as  the  earlier  ones. 
In  the  appendices,  also,  much  matter  has  been  added  relating  to 
works  in  operation,  particularly  to  those  in  America. 

NEW  YORK  January,  1900. 


CONTENTS. 


CHAPTER  I.  INTRODUCTION  i 

II.  CONTINUOUS  FILTERS  AND  THEIR  CONSTRUCTION     .        .      5 

Sedimentation-basins 8 

Size  of  Filter-beds 10 

Covers  for  Filters 12 

III.  FILTERING-MATERIALS 20 

Sand 20 

Gravel 35 

Underdrains 39 

Depth  of  Water  on  Filters 45 

IV.  RATE  OF  FILTRATION  AND  Loss  OF  HEAD          .        .        .47 

Rate  of  Filtration 47 

Loss  of  Head  and  Apparatus  for  regulating  it        .        .     52 

Limit  to  the  Loss  of  Head 60 

V.  CLEANING  FILTERS 68 

Scraping 68 

Frequency  of  Scraping 72 

Sand-washing    .  76 

VI.  THEORY  AND  EFFICIENCY  OF  FILTRATION   .        .        .        .83 

Bacterial  Examination  of  Waters 93 

VII.  INTERMITTENT  FILTRATION 97 

The  Lawrence  Filter 100 

The  Chemnitz  Filter 107 

VIII.  TURBIDITY  AND  COLOR,  AND  THE  EFFECT  OF  MUD  UPON 

SAND  FILTERS 113 

Color 114 

Turbidity  .         .         .         .         .         .         .         .         .         .117 

Preliminary  Processes  to  remove  Mud  .        .        .        -133 

Effect  of  Mud  upon  Sand  Filters 137 

IX.  COAGULATION  OF  WATERS 144 

Substances  used  for  Coagulation 145 

Amount  of  Coagulant  required  to  remove  Turbidity  .  1 50 
Amount  of  Coagulant  required  to  remove  Color  .  .  153 
Successive  Applications  of  Coagulant  .  .  .  .  1 54 
Amount  of  Coagulant  which  Waters  will  receive  .  .155 

vii 


viii  CONTENTS. 

PAGE 

CHAPTER  X.  MECHANICAL  FILTERS 159 

Influence   of   Amount   of  Coagulant  on  Bacterial  Ef- 
ficiency   165 

Types  of  Mechanical  Filters 172 

XL  OTHER  METHODS  OF  FILTRATION 181 

XII.  REMOVAL  OF  IRON  FROM  GROUND-WATERS        .        .        .186 

Cause  of  Iron  in  Ground-waters 187 

Treatment  of  Iron-containing  Waters     .         .         .         .189 
Iron-removal  Plants  in  Operation  .         .         .         .192 

XIII.  TREATMENT  OF  WATERS       . 197 

Cost  of  Filtration 200 

XIV.  WATER-SUPPLY  AND  DISEASE 210 

APPENDIX  I,  GERMAN  OFFICIAL  REGULATION  IN  REGARD  TO  FILTRA- 
TION         .  221 

II.  EXTRACTS    FROM    DR.    REINCKE'S    REPORT    UPON    THE 

HEALTH  OF   HAMBURG  FOR  1892 226 

III.  METHODS  OF  SAND-ANALYSIS 233 

IV.  STATISTICS  OF  SOME  FILTERS 241 

Results  of  Operation 241 

List  of  Sand  Filters  in  Use 244 

List  of  Mechanical  Filters  in  Use    .....  247 
Notes  regarding  Sand  Filters  in  America         .         .         .251 

Extent  of  the  Use  of  Filters 254 

V.  WATER-SUPPLY  OF  LONDON 255 

VI.  WATER-SUPPLY  OF  BERLIN 261 

VII.  WATER-SUPPLY  OF  ALTONA 265 

VIII.  WATER-SUPPLY  OF  HAMBURG 269 

IX.  NOTES  ON  SOME  OTHER  EUROPEAN  SUPPLIES   .        .        .  272 

X.  LITERATURE  OF  FILTRATION 277 

XL  THE  ALBANY  FILTRATION  PLANT 288 

INDEX       • 317 


UNITS   EMPLOYED. 


The  units  used  in  this  work  are  uniformly  those  in  common  use 
in  America,  with  the  single  exception  of  data  in  regard  to  sand-grain 
sizes,  which  are  given  in  millimeters.  The  American  units  were  not 
selected  because  the  author  prefers  them  or  considers  them  partic- 
ularly well  suited  to  filtration,  but  because  he  feared  that  the  use 
of  the  more  convenient  metric  units  in  which  the  very  comprehen- 
sive records  of  Continental  filter  plants  are  kept  would  add  to  the 
difficulty  of  a  clear  comprehension  of  the  subject  by  those  not 
familiar  with  those  units,  and  so  in  a  measure  defeat  the  object  of 
the  book. 

TABLE  OF   EQUIVALENTS. 
Unit.  Metric  Equivalent.  Reciprocal. 

Foot 0.3048  meter  3.2808 

Mile 1609.34      meters  0.0006214 

Acre 4047  square  meters  0.0002471 

Gallon* 3785    liters  0.26417 

i  million  gallons   3785  cubic  meters  0.00026417 

Cubic  yard   0.7645  cubic  meters  1.308 

i  million  gallons  per)          OQ*CA   j  meter  m  depth) 
acre  daily  )  *"   (  of  water  daily     ) 

*The  American  gallon  is  231  cubic  inches  or  0.8333  °f  tne  imperial  gallon.  In 
this  work  American  gallons  are  always  used,  and  English  quantities  are  stated  in 
American,  not  imperial,  gallons. 

ix 


ACKNOWLEDGMENT. 


I  WISH  to  acknowledge  my  deep  obligation  to  the  large  number 
of  European  engineers,  directors,  and  superintendents  of  water- 
works, and  to  the  health  officers,  chemists,  bacteriologists,  and  other 
officials  who  have  kindly  aided  me  in  studying  the  filtration-works 
in  their  respective  cities,  and  who  have  repeatedly  furnished  me  with 
valuable  information,  statistics,  plans,  and  reports. 

To  mention  all  of  them  would  be  impossible,  but  I  wish  particu- 
larly to  mention  Major-General  Scott,  Water-examiner  of  London ; 
Mr.  Mansergh,  Member  of  the  Royal  Commission  on  the  Water- 
supply  of  the  Metropolis ;  Mr.  Bryan,  Engineer  of  the  East  London 
Water  Company  ;  and  Mr.  Wilson,  Manager  of  the  Middlesborough 
Water-works,  who  have  favored  me  with  much  valuable  information. 

In  Holland  and  Belgium  I  am  under  special  obligations  to 
Messrs.  Van  Hasselt  and  Kemna,  Directors  of  the  water  companies 
at  Amsterdam  and  Antwerp  respectively ;  to  Director  Stang  of  the 
Hague  Water-works  ;  to  Dr.  Van't  Hoff,  Superintendent  of  the 
Rotterdam  filters  ;  and  to  my  friend  H.  P.  N.  Halbertsma,  who,  as 
consulting  engineer,  has  built  many  of  the  Dutch  water-works. 

In  Germany  I  must  mention  Profs.  Friihling,  at  Dresden,  and 
Fliigge,  at  Breslau  ;  Andreas  Meyer,  City  Engineer  of  Hamburg; 
and  the  Directors  of  water-works,  Beer  at  Berlin,  Dieckmann  at 
Magdeburg,  Nau  at  Chemnitz,  and  Jockmann  at  Liegnitz,  as  well  as 
the  Superintendent  Engineers  Schroeder  at  Hamburg,  Debusmann 
at  Breslau,  and  Anklamm  and  Piefke  at  Berlin,  the  latter  the  dis- 
tinguished head  of  the  Stralau  works,  the  first  and  most  widely 
known  upon  the  Continent  of  Europe. 

I  have  to  acknowledge  my  obligation  to  City  Engineer  Sechner 
at  Budapest,  and  to  the  Assistant  Engineer  in  charge  of  water-works, 
Kajlinger;  to  City  Engineer  Peters  and  City  Chemist  Bert^chinger 


x  i  i  A  CKNO  WLED  GMENT. 

at  Zurich ;  and  to  Assistant  Engineer  Regnard  of  the  Compagnie 
Generale  des  Eaux  at  Paris. 

On  this  side  of  the  Atlantic  also  I  am  indebted  to  Hiram  K 
Mills,  C.E.,  under  whose  direction  I  had  the  privilege  of  conducting 
for  nearly  five  years  the  Lawrence  experiments  on  filtration  ;  to 
Profs.  Sedgwick  and  Drown  for  the  numerous  suggestions  and 
friendly  criticisms,  and  to  the  latter  for  kindly  reading  the  proof  of 
this  volume ;  to  Mr.  G.  W.  Fuller  for  full  information  in  regard 
to  the  more  recent  Lawrence  results ;  to  Mr.  H.  W.  Clark  for 
the  laborious  examination  of  the  large  number  of  samples  of  sands 
used  in  actual  filters  and  mentioned  in  this  volume;  and  to  Mr. 
Desmond  FitzGerald  for  unpublished  information  in  regard  to  the 
results  of  his  valuable  experiments  on  filtration  at  the  Chestnut  Hill 
Reservoir,  Boston. 

ALLEN  HAZEN. 

BOSTON,  April,  1895. 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


CHAPTER   I. 
INTRODUCTION. 

THE  rapid  and  enormous  development  and  extension  oi 
water-works  in  every  civilized  country  during  the  past  forty 
years  is  a  matter  which  deserves  our  most  careful  consideration, 
as  there  is  hardly  a  subject  which  more  directly  affects  the  health 
and  happiness  of  almost  every  single  inhabitant  of  all  cities  and 
large  towns. 

Considering  the  modern  methods  of  communication,  and  the 
free  exchange  of  ideas  between  nations,  it  is  really  marvellous 
how  each  country  has  met  its  problems  of  water-supply  from  its 
own  resources,  and  often  without  much  regard  to  the  methods 
which  had  been  found  most  useful  elsewhere.  England  has 
secured  a  whole  series  of  magnificent  supplies  by  impounding 
the  waters  of  small  streams  in  reservoirs  holding  enough  water 
to  last  through  dry  periods,  while  on  Continental  Europe  such 
supplies  are  hardly  known.  Germany  has  spent  millions  upon 
millions  in  purifying  turbid  and  polluted  river-waters,  while 
France  and  Austria  have  striven  for  mountain-spring  waters  and 
have  built  hundreds  of  miles  of  costly  aqueducts  to  secure  them. 
In  the  United  States  an  abundant  supply  of  some  liquid  has  too 
often  been  the  objective  point,  and  the  efforts  have  been  most 


2  FILTRATION  OF  PUBLIC    WATER-SUPPLIES, 

successful,  the  American  works  being  entirely  unrivalled  in  the 
volumes  of  their  supplies.  I  do  not  wish  to  imply  that  quality 
has  been  entirely  neglected  in  our  country,  for  many  cities  and 
towns  have  seriously  and  successfully  studied  their  problems, 
with  the  result  that  there  are  hundreds  of  water-supplies  in  the 
United  States  which  will  compare  favorably  upon  any  basis  with 
supplies  in  any  part  of  the  world ;  but  on  the  other  hand  it  is 
equally  true  that  there  are  hundreds  of  other  cities,  including 
some  among  the  largest  in  the  country,  which  supply  their 
citizens  with  turbid  and  unhealthy  waters  which  cannot  be 
regarded  as  anything  else  than  a  national  disgrace  and  a  menace 
to  our  prosperity. 

One  can  travel  through  England,  Belgium,  Holland,  Ger- 
many, and  large  portions  of  other  European  countries  and  drink 
the  water  at  every  city  visited  without  anxiety  as  to  its  effect 
upon  his  health.  It  has  not  always  been  so.  Formerly  Euro- 
pean capitals  drank  water  no  better  than  that  so  often  dis- 
pensed now  in  America.  As  recently  as  1892  Germany's 
great  commercial  centre,  Hamburg,  having  a  water-supply 
essentially  like  those  of  Philadelphia,  Pittsburg,  Cincinnati, 
St.  Louis,  New  Orleans,  and  a  hundred  other  American  cities, 
paid  a  penalty  in  one  month  of  eight  thousand  lives  for  its  care- 
lessness. The  lesson  was  a  dear  one,  but  it  was  not  wasted. 
Hamburg  now  has  a  new  and  wholesome  supply,  and  other  Ger- 
man cities  the  qualities  of  whose  waters  were  open  to  question 
have  been  forced  to  take  active  measures  to  better  their  condi- 
tions. We  also  can  learn  something  from  their  experience. 

There  are  three  principal  methods  of  securing  a  good  water- 
supply  for  a  large  city.  The  first  consists  of  damming  a  stream 
from  an  uninhabited  or  but  sparsely  inhabited  watershed,  thus 
forming  an  impounding  reservoir.  This  method  is  extensively 
used  in  England  and  in  the  United  States.  In  the  latter  most  of 
the  really  good  and  large  supplies  are  so  obtained.  It  is  only 
applicable  to  places  having  suitable  watersheds  within  a  reason- 


INTRODUCTION.  3 

able  distance,  and  there  are  large  regions  where,  owing  to  geo- 
logical and  other  conditions,  it  cannot  be  applied.  It  is  most 
useful  in  hilly  and  poor  farming  countries,  as  in  parts  of  England 
and  Wales,  in  the  Atlantic  States,  and  in  California.  It  cannot 
be  used  to  any  considerable  extent  in  level  and  fertile  countries 
which  are  sure  to  be  or  to  become  densely  populated,  as  is  the 
case  with  large  parts  of  France  and  Germany  and  in  the  Middle 
States. 

The  second  method  is  to  secure  ground-water,  that  is,  spring 
or  well  water,  which  by  its  passage  through  the  ground  has 
become  thoroughly  purified  from  any  impurities  which  it  may 
have  contained.  This  was  the  earliest  and  is  the  most  widely 
used  method  of  securing  good  water.  It  is  specially  adapted 
to  small  supplies.  Under  favorable  geological  conditions  very 
large  supplies  have  been  obtained  in  this  manner.  In  Europe 
Paris,  Vienna,  Budapest,  Munich,  Cologne,  Leipzig,  Dresden, 
a  part  of  London,  and  very  many  smaller  places  are  so  supplied. 
This  method  is  also  extensively  used  in  the  United  States  for 
small  and  medium-sized  places,  and  deserves  to  be  most  care- 
fully studied,  and  used  whenever  possible,  but  is  unfortunately 
limited  by  geological  conditions  and  cannot  be  used  except  in 
a  fraction  of  the  cases  where  supplies  are  required.  No  ground- 
water  supplies  yet  developed  in  the  United  States  are  comparable 
in  size  to  those  used  in  Europe. 

The  third  process  of  securing  a  good  water-supply  is  by  means 
of  filtration  of  surface  waters  which  would  otherwise  be  unsuit- 
able for  domestic  purposes.  The  methods  of  filtration,  which  it 
is  the  purpose  of  this  volume  to  explain,  are  beyond  the  experi- 
mental stage  ;  they  are  now  applied  to  the  purification  of  the 
water-supplies  of  European  cities  with  an  aggregate  population 
of  at  least  20,000,000  people.  In  the  United  States  the  use  of 
filters  is  much  less  common,  and  most  of  the  filters  in  use  are  of 
comparatively  recent  installation. 

Great  interest  has  been   shown  in  the  subject  during  the  last 


4  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

few  years,  and  the  peculiar  character  of  some  American  waters, 
which  differ  widely  in  their  properties  from  those  of  many 
European  streams,  has  received  careful  and  exhaustive  considera- 
tion. In  Europe  filtration  has  been  practised  with  continually 
improving  methods  since  1829,  and  the  process  has  steadily  re- 
ceived wider  and  wider  application.  It  has  been  most  searchingly 
Investigated  in  its  hygienic  relations,  and  has  been  repeatedly 
found  to  be  a  most  valuable  aid  in  reducing  mortality.  The  con- 
ditions under  which  satisfactory  results  can  be  obtained  are  now 
tolerably  well  known,  so  that  filters  can  be  built  in  the  United 
States  with  the  utmost  confidence  that  the  result  will  not  be 
disappointing. 

The  cost  of  filtration,  although  considerable,  is  not  so  great 
as  to  put  it  beyond  the  reach  of  American  cities.  It  may  be 
roughly  estimated  that  the  cost  of  filtration,  with  all  necessary 
interest  and  sinking  funds,  will  add  10  per  cent  to  the  average 
cost  of  water  as  at  present  supplied. 

It  may  be  confidently  expected  that  when  the  facts  are  better 
understood  and  realized  by  the  American  public,  we  shall 
abandon  the  present  filthy  and  unhealthy  habit  of  drinking 
polluted  river  and  lake  waters,  and  shall  put  the  quality  as  well 
as  the  quantity  of  our  supplies  upon  a  level  not  exceeded  by 
those  of  any  country. 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION. 


CHAPTER  II. 
CONTINUOUS  FILTERS  AND  THEIR  CONSTRUCTION. 

FILTRATION  of  water  consists  in  passing  it  through  some 
substance  which  retains  or  removes  some  of  its  impurities.  In 
its  simplest  form  filtration  is  a  straining  process,  and  the  results 
obtained  depend  upon  the  fineness  of  the  strainer,  and  this  in 
turn  is  regulated  by  the  character  of  the  water  and  the  uses  to 
which  it  is  to  be  put.  Thus  in  the  manufacture  of  paper  an 
enormous  volume  of  water  is  required  free  from  particles  which, 
if  they  should  become  imbedded  in  the  paper,  would  injure  its 
appearance  or  texture.  Obviously  for  this  purpose  the  removal 
of  the  smaller  particles  separately  invisible  to  the  unaided  eye,  and 
thus  not  affecting  the  appearance  of  the  paper,  and  the  removal 
of  which  would  require  the  use  of  a  finer  filter  at  increased 
expense,  would  be  a  simple  waste  of  money.  When,  however, 
a  water  is  to  be  used  for  a  domestic  water  supply  and  transpar- 
ency is  an  object,  the  still  finer  particles  which  would  not  show 
themselves  in  paper,  but  which  are  still  able,  in  bulk,  to  render  a 
water  turbid,  should  be  as  far  as  possible  removed,  thus  necessi- 
tating a  finer  filter ;  and,  when  there  is  reason  to  think  that  the 
water  contains  the  germs  of  disease,  the  filter  must  be  fine 
enough  to  remove  with  certainty  those  organisms  so  extraordi- 
narily small  that  millions  of  them  may  exist  in  a  glass  of  water 
without  imparting  a  visible  turbidity. 

It  is  now  something  over  half  a  century  since  the  first  suc- 
cessful attempts  were  made  to  filter  public  water-supplies,  and 
there  are  now  hundreds  of  cities  supplied  with  clear,  healthy, 
filtered  water.  (Appendix  IV.)  While  the  details  of  the  filters 


O  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

used  in  different  places  present  considerable  variations,  the  general 
form  is,  in  Europe  at  least,  everywhere  the  same.  The  most  im- 
portant parts  of  a  filter  are  shown  by  the  accompanying  sketch, 


FIG.  i. — SKETCH  SHOWING  GENERAL  ARRANGEMENT  OF  FILTER  PLANTS. 

in  which  the  dimensions  are  much  exaggerated.  The  raw  water 
is  taken  from  the  river  into  a  settling-basin,  where  the  heaviest 
mud  is  allowed  to  settle.  In  the  case  of  lake  and  pond  waters 
the  settling-tank  is  dispensed  with,  but  it  is  essential  for  turbid 
river-water,  as  otherwise  the  mud  clogs  the  filter  too  rapidly. 
The  partially  clarified  water  then  passes  to  the  filter,  which 
consists  of  a  horizontal  layer  of  rather  fine  sand  supported  by 
gravel  and  underdrained,  the  whole  being  enclosed  in  a  suita- 
ble basin  or  tank.  The  water  in  passing  through  the  sand  leaves 
behind  upon  the  sand  grains  the  extremely  small  particles  which 
were  too  fine  to  settle  out  in  the  settling-basin,  and  is  quite  clear 
as  it  goes  from  the  gravel  to  the  drains  and  the  pumps,  which 
forward  it  to  the  reservoir  or  city. 

The  passages  between  the  grains  of  sand  through  which  the 
water  must  pass  are  extremely  small.  If  the  sand  grains  were 
spherical  and  -^  of  an  inch  in  diameter,  the  openings  would  only 
allow  the  passage  of  other  spheres  ¥^  of  an  inch  in  diameter, 
and  with  actual  irregular  sands  much  finer  particles  are  held 
back.  As  a  result  the  coarser  matters  in  the  water  are  re- 
tained on  the  surface  of  the  sand,  where  they  quickly  form  a 
layer  of  sediment,  which  itself  becomes  a  filter  much  finer  than 
the  sand  alone,  and  which  is  capable  of  holding  back  under  suit- 
able conditions  even  the  bacteria  of  the  passing  water.  The 
water  which  passes  before  this  takes  place  may  be  less  perfectly 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION.  7 

filtered,  but  even  then,  the  filter  may  be  so  operated  that  nearly 
all  of  the  bacteria  will  be  deposited  in  the  sand  and  not  allowed 
to  pass  through  into  the  effluent. 

As  the  sediment  layer  increases  in  thickness  with  continued 
filtration,  increased  pressure  is  required  to  drive  the  desired 
volume  of  water  through  its  pores,  which  are  ever  becoming 
smaller  and  reduced  in  number.  When  the  required  quantity 
of  water  will  no  longer  pass  with  the  maximum  pressure  allowed, 
it  is  necessary  to  remove,  by  scraping,  the  sediment  layer,  which 
should  not  be  more  than  an  inch  deep.  This  layer  contains  most 
of  the  sediment,  and  the  remaining  sand  will  then  act  almost  as 
new  sand  would  do.  The  sand  removed  may  be  washed  for  use 
again,  and  eventually  replaced  when  the  sand  layer  becomes  too 
thin  by  repeated  scrapings.  These  operations  require  that  the 
filter  shall  be  temporarily  out  of  use,  and  as  water  must  in 
general  be  supplied  without  intermission,  a  number  of  filters  are 
built  together,  so  that  any  of  them  can  be  shut  out  without 
interfering  with  the  action  of  the  others. 

The  arrangement  of  filters  in  relation  to  the  pumps  varies 
with  local  conditions.  With  gravity  supplies  the  filters  are 
usually  located  below  the  storage  reservoir,  and,  properly  placed, 
involve  only  a  few  feet  loss  of  head. 

In  the  case  of  tidal  rivers,  as  at  Antwerp  and  Rotterdam, 
the  quality  of  the  raw  water  varies  with  the  tide,  and  there  is  a 
great  advantage  in  having  the  settling-basins  low  enough  so 
that  a  whole  day's  supply  can  be  rapidly  let  in  when  the 
water  is  at  its  best,  without  pumping.  At  Antwerp  the  filters 
are  higher,  and  the  water  is  pumped  from  the  settling  basins  to 
them,  and  again  from  the  reservoir  receiving  the  effluents  from 
the  filters  to  the  city.  In  several  of  the  London  works  (East 
London,  Grand  Junction,  Southwark  and  Vauxhall,  etc.)  the 
settling-basins  are  lower  than  the  river,  and  the  filters  are  still 
lower,  so  that  a  single  pumping  suffices,  that  coming  between 
the  filter  and  the  city,  or  elevated  distributing  reservoir. 


8  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

In  many  other  English  niters  and  in  most  German  works  the 
settling-basins  and  niters  are  placed  together  a  little  higher  than 
the  river,  thus  avoiding  at  once  trouble  from  floods  and  cost 
for  excavation.  The  water  requires  to  be  pumped  twice,  once 
before  and  once  after  nitration.  At  Altona  the  settling-basins  and 
filters  are  placed  upon  a  hill,  to  which  the  raw  Elbe  water  is 
pumped,  and  from  which  it  is  supplied  to  the  city  after  filtration 
by  gravity  without  further  pumping.  The  location  of  the  works 
in  this  case  is  said  to  have  been  determined  by  the  location  of 
a  bed  of  sand  suitable  for  filtration  on  the  spot  where  the  filters 
were  built. 

When  two  pumpings  are  required  they  are  frequently  done, 
especially  in  the  smaller  places,  in  the  same  pumping-station, 
with  but  one  set  of  boilers  and  engines,  the  two  pumps  being 
connected  to  the  same  engine.  The  cost  is  said  to  be  only 
slightly  greater  than  that  of  a  single  lift  of  the  same  total  height. 
In  very  large  works,  as  at  Berlin  and  Hamburg  and  some  of 
the  London  companies,  two  separate  sets  of  pumping  machinery 
involve  less  extra  cost  relatively  than  would  be  the  case  with 
smaller  works. 

SEDIMENTATION-BASINS. 

Kirkvvood  *  found  in  1866  that  sedimentation-basins  were  es- 
sential to  the  successful  treatment  of  turbid  river-waters,  and 
subsequent  experience  has  not  in  any  way  shaken  his  conclusion. 
The  German  works  visited  by  him,  Berlin  (Stralau)  and  Altona, 
were  both  built  by  English  engineers,  and  their  settling-basins 
did  not  differ  materially  from  those  of  corresponding  works  in 
England.  Since  that  time,  however,  there  has  been  a  well- 
marked  tendency  on  the  part  of  the  German  engineers  to  use 
smaller,  while  the  English  engineers  have  used  much  larger  sedi- 
mentation-basins, so  that  the  practices  of  the  two  countries  are 

*  Filtration  of  River  Waters.     Van  Nostrand  &  Co.,  1869. 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION.  9 

now  widely  separated,  the  difference  no  doubt  being  in  part  at 
least  due  to  local  causes. 

Kirkwood  found  sedimentation-basins  at  Altona  with  a  capac- 
ity of  2j  times  the  daily  supply.  In  1894  the  same  basins 
were  in  use,  although  the  filtering  area  had  been  increased 
from  0.82  acre  to  2.20  acres,  and  still  more  niters  were  in  course 
of  construction,  and  the  average  daily  quantity  of  water  had  in- 
creased from  600,000  to  4,150,000  gallons  in  1891-2,  or  more  than 
three  times  the  capacity  of  the  sedimentation-basins.  In  1890 
the  depth  of  mud  deposited  in  these  basins  was  reported  to  be 
two  feet  deep  in  three  months.  At  Stralau  in  Berlin,  also,  in 
the  same  time  the  filtering  area  was  nearly  doubled  without  in- 
creasing the  size  of  the  sedimentation-basins,  but  the  Spree  at 
this  point  has  such  a  slow  current  that  it  forms  itself  a  natural 
sedimentation-basin.  At  Magdeburg  on  the  Elbe  works  were 
built  in  1876  with  a  filtering  area  of  1.92  acres,  and  a  sedimen- 
tation-basin capacity  of  11,300,000  gallons,  but  in  1894  half  of  the 
latter  had  been  built  over  into  filters,  which  with  two  other  filters 
gave  a  total  filtering  surface  of  3.90  acres,  with  a  sedimentation- 
basin  capacity  of  only  5,650,000  gallons.  The  daily  quantity  of 
water  pumped  for  1891-2  was  5,000,000  gallons,  so  that  the  pres- 
ent sedimentation-basin  capacity  is  about  equal  to  one  day's 
supply,  or  relatively  less  than  a  third  of  the  original  provision. 
The  idea  followed  is  that  most  of  the  particles  which  will  settle 
at  all  will  do  so  within  twenty-four  hours,  and  that  a  greater 
storage  capacity  may  allow  the  growth  of  algae,  and  that  the 
water  may  deteriorate  rather  than  improve  in  larger  tanks. 

At  London,  on  the  other  hand,  the  authorities  consider  a 
large  storage  capacity  for  unfiltered  water  as  one  of  the  most 
important  conditions  of  successful  filtration,  the  object  however,, 
being  perhaps  as  much  to  secure  storage  as  to  allow  sedimenta- 
tion. In  1893  thirty-nine  places  were  reported  upon  the  Thames 
and  the  Lea  which  were  giving  their  sewage  systematic  treat- 
ment before  discharging  it  into  the  streams  from  which  London's 


10  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

water  is  drawn.  These  sewage  treatments  are,  with  hardly  an 
exception,  dry-weather  treatments,  and  as  soon  as  there  is  a  con- 
siderable storm  crude  sewage  is  discharged  into  the  rivers  at 
every  point.  The  rivers  are  both  short,  and  are  quickly  flooded, 
and  afterwards  are  soon  back  in  their  usual  condition.  At  these 
times  of  flood,  the  raw  water  is  both  very  turbid  and  more 
polluted  by  sewage  than  at  other  times,  and  it  is  the  aim  of  the 
authorities  to  have  the  water  companies  provide  reservoir  capac- 
ity enough  to  carry  them  through  times  of  flood  without  draw- 
ing any  water  whatever  from  the  rivers.  This  obviously  involves 
much  more  extensive  reservoirs  than  those  used  in  Germany,  and 
the  companies  actually  have  large  basins  and  are  still  adding 
to  them.  The  storage  capacities  of  the  various  companies  vary 
from  3  to  1 8  times  the  respective  average  daily  supplies,  and 
together  equal  9  times  the  total  supply. 

In  case  the  raw  water  is  taken  from  a  lake  or  a  river  at  a 
point  where  there  is  but  little  current,  as  in  a  natural  or  artificial 
pond,  sedimentation-basins  are  unnecessary.  This  is  the  case  at 
Zurich  (lake  water),  at  Berlin  when  the  rivers  Havel  and  Spree 
spread  into  lakes,  at  Tegel  and  Miiggel,  and  at  numerous  other 
works. 

SIZE   OF   FILTER-BEDS. 

The  total  area  of  filters  required  in  any  case  is  calculated 
from  the  quantity  of  water  required,  the  rate  of  filtration,  and  an 
allowance  for  filters  out  of  use  while  being  cleaned.  To  prevent 
interruptions  of  the  supply  at  times  of  cleaning,  the  filtering  area 
is  divided  into  beds  which  are  operated  separately,  the  number 
and  size  of  the  beds  depending  upon  local  conditions.  The  cost 
per  acre  is  decreased  with  large  beds  on  account  of  there  being 
less  wall  or  embankment  required,  while,  on  the  other  hand,  the 
convenience  of  operation  may  suffer,  especially  in  small  works.  It 
is  also  frequently  urged  that  with  large  filters  it  is  difficult  or  im- 
possible to  get  an  even  rate  of  filtration  over  the  entire  area  ow. 


PAVED  EMBANKMENT  BETWEEN  Two  FILTERS,  EAST  LONDON. 


FILTERS  AND  CHANNELS  FOR  RAW  WATER,  ANTWERP. 

\Tofacepage  10.] 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION.          II 

ing  to  the  frictional  resistance  of  the  underdrains  for  the  more 
distant  parts  of  the  filter.  A  discussion  of  this  point  is  given  in 
Chapter  III,  page  41.  At  Hamburg,  where  the  size  of  the  single 
beds,  1.88  acres  each,  is  larger  than  at  any  other  place,  it  is  shown 
that  there  is  no  serious  cause  for  anxiety  ;  and  even  if  there  were, 
the  objectionable  resistance  could  be  still  farther  reduced  by  a 
few  changes  in  the  under-drains.  The  sizes  of  filter-beds  used 
at  a  large  number  of  places  are  given  in  Appendix  IV. 

At  a  number  of  places  having  severe  winters,  filters  are 
vaulted  over  as  a  protection  from  cold,  and  in  the  most  important 
of  these,  Berlin,  Warsaw,  and  St.  Petersburg,  the  areas  of  the 
single  beds  are  nearly  the  same,  namely,  from  0.52  to  0.59  acre. 
The  works  with  open  filters  at  London  (seven  companies),  Am- 
sterdam, and  Breslau  have  filter-beds  from  0.82  to  1.50  acres  each. 
Liverpool  and  Hamburg  alone  use  filters  with  somewhat  larger 
areas.  Large  numbers  of  works  with  both  covered  and  open 
filters  have  much  smaller  beds  than  these  sizes,  but  generally  this 
is  to  avoid  too  small  a  number  of  divisions  in  a  small  total  area, 
although  such  works  have  sometimes  been  extended  with  the 
growth  of  the  cities  until  they  now  have  a  considerable  number 
of  very  small  basins. 


FORM   OF   FILTER-BEDS. 

The  form  and  construction  of  the  filter-beds  depend  upon 
local  conditions,  the  foundations,  and  building  materials  available, 
the  principles  governing  these  points  being  in  general  the  same 
as  for  the  construction  of  ordinary  reservoirs.  The  bottoms  re- 
quire to  be  made  water-tight,  either  by  a  thin  layer  of  concrete 
or  by  a  pavement  upon  a  puddle  layer.  For  the  sides  either 
masonry  walls  or  embankments  are  used,  the  former  saving 
space,  but  being  in  general  more  expensive  in  construction. 
Embankments  must,  of  course,  be  substantially  paved  near  the 


12  FILTRATION   OF  PUBLIC   WATER-SUPPLIES. 

water-line  to  withstand  the  action  of  ice,  and  must  not  be  injured 
by  rapid  fluctuations  in  the  water-levels  in  the  filters. 

Failure  to  make  the  bottoms  water-tight  has  perhaps  caused 
more  annoyance  than  any  other  single  point.  With  a  leaky  bot- 
tom there  is  either  a  loss  of  water  when  the  water  in  the  filters 
is  higher  than  the  ground-water,  or  under  reverse  conditions,  the 
ground-water  comes  in  and  mixes  with  the  filtered  water,  and 
the  latter  is  rarely  improved  and  may  be  seriously  damaged  by 
the  admixture.  And  with  very  bad  conditions  water  may  pass 
from  one  filter  to  another,  with  the  differences  in  pressure  always 
existing  in  neighboring  filters,  with  most  unsatisfactory  results. 


COVERS    FOR   FILTERS. 

The  filters  in  England  and  Holland  are  built  open,  without 
protection  from  the  weather.  In  Germany  the  filters  first  built 
were  also  open,  but  in  the  colder  climates  more  or  less  difficulty 
was  experienced  in  keeping  the  filters  in  operation  in  cold 
weather.  An  addition  to  the  Berlin  filters,  built  in  1874,  was 
covered  with  masonry  vaulting,  over  which  several  feet  of  earth 
were  placed,  affording  a  complete  protection  against  frost.  The 
filters  at  Magdeburg  built  two  years  later  were  covered  in  the 
same  way,  and  since  that  time  covered  filters  have  been  built 
at  perhaps  a  dozen  different  places. 

It  was  found  at  Berlin  that,  owing  to  the  difficulty  of  properly 
cleaning  the  open  filters  in  winter,  it  was  impossible  to  keep  the 
usual  proportion  of  the  area  in  effective  service,  and  as  a  result 
portions  of  the  filters  were  greatly  overtaxed  during  prolonged 
periods  of  cold  weather.  This  resulted  in  greatly  decreased 
bacterial  efficiency,  the  bacteria  in  March,  1889,  reaching  3000  to 
4000  per  cc.  (with  100,000  in  the  raw  water),  although  ordinarily 
the  effluent  contained  less  than  100.  An  epidemic  of  typhoid 
fever  followed,  and  was  confined  to  that  part  of  the  city  supplied 


INTERIOR  VIEW  OF  COVERED  FILTER,  ASHLAND,  Wis. 
When  in  use  the  water  rises'  nearly  to  the  springing  line  of  the  arches. 


COVERED    FILTER   IN    COURSE    OF   CONSTRUCTION,    SHOWING  WOODEN    CENTERS 
FOR  MASONRY  VAULTING,  SOMERSWORTH,  N.  H. 

[  70  face  page  12.] 


*cPe 
rf£*  OF  THB 

UNIVERSITY 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION.  13 

from  the  Stralau  works,  the  wards  supplied  from  the  covered 
Tegel  filters  remaining  free  from  fever.  Open  filters  have  since 
been  abandoned  in  Berlin. 

At  Altona  also,  where  the  water  is  taken  from  an  excessively 
polluted  source,  decreased  bacterial  efficiency  has  repeatedly 
resulted  in  winter,  and  the  occasional  epidemics  of  typhoid  fever 
in  that  city,  which  have  invariably  come  in  winter,  appear  to  have 
been  directly  due  to  the  effect  of  cold  upon  the  open  filters. 
The  city  has  just  extended  the  open  filters,  and  hopes  with  an 
increased  reserve  area  to  avoid  the  difficulty  in  future  without 
resource  to  covered  filters.  (See  Appendices  II  and  VII.) 

Brunswick,  Liibeck,  and  Frankfort  on  Oder  with  cold  winters 
have  open  filters,  but  draw  their  water-supplies  from  less  pol- 
luted sources,  and  have  thus  far  escaped  the  fate  of  Berlin  and 
Altona.  The  new  filters  at  Hamburg  also  are  open.  At  Zurich, 
where  open  and  covered  filters  were  long  used  side  by  side,  the 
covered  filters  were  much  more  satisfactory,  and  the  old  open 
filters  have  recently  been  vaulted  over. 

Konigsberg  originally  built  open  filters,  but  was  afterward 
obliged  to  cover  them,  on  account  of  the  severe  winters;  and  at 
Breslau,  where  open  filters  have  long  been  used,  the  recent  ad- 
ditions are  vaulted  over. 

The  fact  that  inferior  efficiency  of  filtration  results  with  open 
filters  during  prolonged  and  severe  winter  weather  is  generally 
admitted,  although  there  is  some  doubt  as  to  the  exact  way  in 
which  the  disturbance  is  caused.  In  some  works  I  am  informed 
that  in  cutting  the  ice  around  the  edges  of  the  filter  and  re- 
peatedly piling  the  loose  pieces  upon  the  floating  cake,  the  latter 
eventually  becomes  so  thickened  at  the  sides  that  the  projecting 
lower  corners  actually  touch  the  sand,  with  the  fluctuating  levels 
which  often  prevail  in  these  works,  and  that  in  this  way  the 
sediment  layer  upon  the  top  of  the  sand  is  broken  and  the  water 
rapidly  passes  without  adequate  purification  at  the  points  of  dis- 
turbance. 


14  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

This  theory  is,  however,  inadequate  to  account  for  many 
cases  where  such  an  accumulation  of  ice  is  not  allowed.  In 
these  cases  the  poor  work  is  not  obtained  until  after  the  niters 
have  been  scraped.  The  sand  apparently  freezes  slightly  while 
the  water  is  off,  and  when  water  is  brought  back  and  filtration 
resumed,  normal  results  are  for  some  reason  not  again  obtained 
for  a  time. 

In  addition  to  the  poorer  work  from  open  filters  in  cold 
weather,  the  cost  of  removing  the  ice  adds  materially  to  the 
operating  expenses,  and  in  very  cold  climates  would  in  itself 
make  covers  advisable. 

I  have  arranged  the  European  filter  plants,  in  regard  to- 
which  I  have  sufficient  information,  in  the  table  on  page  15,  in 
the  order  of  the  normal  mean  January  temperatures  of  the 
respective  places.  This  may  not  be  an  ideal  criterion  of  the 
necessity  of  covering  filters,  but  it  is  at  least  approximate,  and  in 
the  absence  of  more  detailed  comparisons  it  will  serve  to  give  a 
good  general  idea  of  the  case.  I  have  not  found  a  single  case 
where  covered  filters  are  used  where  the  January  temperature 
is  32°  F.  or  above.  In  some  of  these  places  some  trouble  is  ex- 
perienced in  unusually  cold  weather,  but  I  have  not  heard  of  any 
very  serious  difficulty  or  of  any  talk  of  covering  filters  at  these 
places  except  at  Rotterdam,  where  a  project  for  covering  was 
being  discussed. 

Those  places  having  January  temperatures  below  30°  experi- 
ence a  great  deal  of  difficulty  with  open  filters  ;  so  much  so,  that 
covered  filters  may  be  regarded  as  necessary  for  them,  although 
it  is  possible  to  keep  open  filters  running  with  decreased  effi- 
ciency and  increased  expense  by  freely  removing  the  ice,  with 
January  temperatures  some  degrees  lower. 

Where  the  mean  January  temperature  is  30°  to  32°  F.  there  is 
room  for  doubt  as  to  the  necessity  of  covering  filters,  but,  judging 
from  the  experience  of  Berlin  and  Altona,  the  covered  filters 
are  much  safer  at  this  temperature. 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION.          1 5 
TABLE    OF    PLACES    HAVING    OPEN    AND    COVERED    FILTERS. 
ARRANGED  ACCORDING  TO  THE  MEAN  JANUARY  TEMPERATURES. 


Normal  Mean 
January 
Temperature. 
Degrees  F. 

Place. 

Kind  of  Filters  and  Results. 

37-40° 

All  English  cities 

Open  filters  only  are  used,  and  no  great 

difficulty  with  ice  is  experienced. 

33-35° 

Cities  in  Holland 

All  filters  are  open,  and  there  is  little  se- 

rious trouble  with  ice  ;  but  at  Amster- 

dam  and  Rotterdam   the   bacteria  in 

effluents  are  said  to  be  higher  in  winter 

than  at  other  times. 

32° 

Bremen 

Open  filters. 

31° 

Altona 

Much  difficulty  with  ice  in   open   filters 

(see  Appendices  II  and  VII). 

31° 

Brunswick 

Open  filters. 

3i° 

Hamburg 

"         " 

3'° 

Lubeck 

it         « 

3i° 

Berlin 

Open  filters  were  formerly  used,  but  owing 

to  decreased  efficiency  in  cold  weather 

they  have  been  abandoned  for  covered 

ones. 

3i° 

Magdeburg 

Covered  filters,  but  a  recent  addition  is 

not  covered. 

30° 

Frankfort  on  Oder 

Open  filters. 

30° 

Stuttgart 

Part  of  the  filters  are  covered. 

30° 

Stettin 

"        "          "         "          " 

29° 

Zurich 

Covered  filters  were  much  the  most  satis- 

factory, and  the  open  ones  were  cov- 

ered   in    1894.     The   raw  water  has  a 

temperature  of  35°. 

29° 

Liegnitz 

Open  filters. 

29° 

Breslau 

Open   filters  have  been  used,  but  recent 

additions  are  covered. 

29° 

Budapest 

Covered  filters  only. 

29° 

Posen 

«             it         it 

26° 

Konigsberg 

The  original  filters  were  open,  but  it  was 

found  necessary  to  cover  them. 

24° 

Warsaw 

Covered  filters  only. 

1  6° 

St.  Petersburg 

ii            it         it 

In  case  the  raw  water  was  drawn  from  a  lake  at  a  depth 
where  its  minimum  temperature  was  above  32°,  which  is  the 
temperature  which  must  ordinarily  be  expected  in  surface-waters 
in  winter,  open  niters  might  be  successfully  used  in  slightly 
colder  places. 

The  covers  are  usually  of  brick  or  concrete  vaulting   sup- 


56  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

ported  by  pillars  at  distances  of  11  to  15  feet  in  each  direction, 
the  whole  being  covered  by  2  or  3  feet  of  earth  ;  and  the  top 
can  be  laid  out  as  a  garden  if  desired.  Small  holes  for  the 
admission  of  air  and  light  are  usually  left  at  intervals.  The 
thickness  of  the  masonry  and  the  sizes  of  the  pillars  used  in 
some  of  the  earlier  German  vaultings  are  unnecessarily  great, 
and  some  of  the  newer  works  are  much  lighter.  For  American 
use,  vaulting  like  that  used  for  the  Newton,  Mass.,  covered  reser- 
voir* should  be  amply  strong. 

Roofs  have  been  used  at  Konigsberg,  Posen,  and  Budapest 
instead  of  the  masonry  vaulting.  They  are  cheaper,  but  do  not 
afford  as  good  protection  against  frost,  and  even  with  great  care 
some  ice  will  form  under  them. 

Provision  must  be  made  for  entering  the  niters  freely  to 
introduce  and  remove  sand.  This  is  usually  accomplished  by 
raising  one  section  of  vaulting  and  building  a  permanent  incline 
under  it  from  the  sand  line  to  a  door  above  the  high-water  line 
in  the  filter. 

The  cost  of  building  covered  filters  is  said  to  average  fully 
one  half  more  than  open  filters. 

Among  the  incidental  advantages  of  covered  filters  is  that 
with  the  comparative  darkness  there  is  no  tendency  to  algas 
growths  on  the  filters  in  summer,  and  the  frequency  of  scraping 
is  therefore  somewhat  reduced.  At  Zurich,  in  1892,  where  both 
covered  and  open  filters  were  in  use  side  by  side,  the  periods 
between  scrapings  averaged  a  third  longer  in  the  covered  than 
in  the  open  filters. 

It  has  been  supposed  that  covered  filters  kept  the  water  cool 
in  summer  and  warm  in  winter,  but  owing  to  the  large  volume 
of  water  passing,  the  change  in  temperature  in  any  case  is  very 
slight ;  Fruhling  found  that  even  in  extreme  cases  a  change  of 
over  3°  F.  in  either  direction  is  rarely  observed. 

*  Annual  Report  of  Albert  F.  Noyes,  City  Engineer  for  1891. 


x  - 

c.   ~ 


CONTINUOUS  FILTERS  AND    THEIR   CONSTRUCTION. 


^At  Berlin,  where  open  and  covered  filters  were  used  side  by 
side  "It*  Stralau  for  twenty  years,  it  was  found  that,  bacteri- 
ally,the  d^n  filters  were,  except  in  severe  winter  weather,  more 
efficient.  It  V/as  long  supposed  that  this  was  caused  by  the  ster- 
ilizing action  of  the  sunlight  upon  the  water  in  the  open  filters. 
This  result,  however,  was  not  confirmed  elsewhere,  and  it  was 
finally  discovered,  in  1893,  that  the  higher  numbers  were  due  to 
the  existence  of  passages  in  corners  on  the  columns  of  the 
vaulted  roof  and  around  the  ventilators  for  the  underdrains, 
through  which,  practically,  unfiltered  water  found  its  way  into 
the  effluent.  This  at  once  removes  the  evidence  in  favor  of 
the  superior  bacterial  efficiency  of  open  filters  and  suggests  the 
necessity  of  preventing  such  passages.  The  construction  of  a 
ledge  all  around  the  walls  and  pillars  four  inches  wide  and  a 
little  above  the  gravel,  as  shown  in  the  sketch,  might  be  useful 
in  this  way,  and  the  slight  lateral 
movement  of  the  water  in  the 
sand  above  would  be  of  no  con- 
sequence. The  sand  would  evi- 
dently make  a  closer  joint  with 
the  horizontal  ledge  than  with  the 
vertical  wall. 

In  regard  to  the  probable  re- 
quirement or  advisability  of  covers 
for  filters  in  the  United  States,  I 
judge,  from  the  European  experi- 
ence, that  places  having  January 
temperatures  below  the  freezing-  FIG.  2. 

point  will  have  considerable  trouble  from  open  filters,  and  would 
best  have  covered  filters.  Places  having  higher  winter  tempera- 
tures will  be  able  to  get  along  with  the  ice  which  may  form  on 
open  filters,  and  the  construction  of  covers  would  hardly  be  ad- 
visable except  under  exceptional  local  conditions,  as,  for  instance, 
with  a  water  with  an  unusual  tendency  to  algae  growths. 


1 8  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

I  have  drawn  a  line  across  a  map  of  the  United  States  on  this 
basis  (shown  by  the  accompanying  plate)  and  it  would  appear  that 
places  far  north  of  the  line  would  require  covered  filters,  and  that 
those  south  of  it  would  not,  while  for  the  places  in 'the  immediate 
vicinity  of  the  line  (comparable  to  Hamburg  and  Altona)  there  is 
room  for  discussion. 

In  the  United  States  covered  filters  have  been  constructed 
at  St.  Johnsbury,  Vt.,  Somersworth,  N.  H.,  Albany,  N.  Y., 
Ashland,  Wis.,  and  Grand  Forks,  N.  Dak.,  all  of  these  places 
being  considerably  north  of  the  above-mentioned  line. 

The  filter  at  Lawrence,  Mass.,  with  a  mean  January  tempera- 
ture of  about  25°,  is  not  covered,  but  serious  difficulty  and  expense 
have  been  experienced  at  times  from  the  ice,  so  much  so  that  it 
has  been  repeatedly  recommended  to  cover  it.  Open  filters  have 
also  been  in  use  for  many  years  at  Hudson  and  Poughkeepsie, 
N.  Y.,  with  mean  January  temperatures  about  24°;  and  although 
considerable  difficulty  has  been  experienced  from  ice  at  times, 
these  filters,  particularly  the  ones  at  Poughkeepsie,  have  been  kept 
in  very  serviceable  condition  at  all  times,  notwithstanding  the  ice. 

At  Mount  Vernon,  N.  Y.,  with  a  mean  January  temperature 
of  about  31°,  and  with  a  reservoir  water,  no  serious  difficulty  has 
been  experienced  with  ice;  and  at  Far  Rockaway,  L.  I.,  with  a 
slightly  higher  temperature  and  well-water,  no  difficulty  whatever 
has  been  experienced  with  open  filters.  Filters  at  Ilion,  N.  Y., 
with  a  mean  January  temperature  of  about  23°,  are  not  covered, 
and  are  fed  from  a  reservoir.  No  serious  difficulty  has  been 
experienced  with  ice,  which  is  probably  due  to  the  fact  that 
the  water  applied  to  them  is  taken  from  near  the  bottom  of  the 
reservoir,  and  ordinarily  has  a  temperature  somewhat  above  the 
freezing-point  throughout  the  winter. 

The  cost  of  removing  ice  from  filters  depends,  among  other 
things,  upon  the  amount  of  reserve  filter  area.  When  this  reserve 
is  small  the  filters  must  be  kept  constantly  at  work  nearly  up  to 
their  rated  capacity;  the  ice  must  be  removed  promptly  whenever 


4-2.6 

AtSILENt 


Map    showing' 

Normal  Mean   January  Temperatures 

IN  THE  UNITED    STATES 

and   theArea  in  which    Filters    should    be     covered 


RAJ 


51. 

•  SANANTONIO 


CONTINUOUS  FILTERS  AND    THEIR    CONSTRUCTION.          19 

the  filters  require  cleaning,  and  under  some  conditions  the  expense 
of  doing  this  may  be  considerable.  If,  on  the  other  hand,  there 
is  a  considerable  reserve  area,  so  that  when  a  filter  becomes  clogged 
in  severe  weather,  the  work  can  be  turned  upon  other  filters  and 
the  clogged  filter  allowed  to  remain  until  more  moderate  weather, 
or  until  a  thaw,  the  expense  of  ice  removal  may  be  kept  at  a 
materially  lower  figure. 

In  case  open  filters  are  built  near  or  north  of  this  line,  I  would 
suggest  that  plenty  of  space  between  and  around  the  filters  for 
piling  up  ice  in  case  of  necessity  may  be  found  advantageous,  and 
that  a  greater  reserve  of  filtering  area  for  use  in  emergencies  should 
be  provided  than  would  be  considered  necessary  with  vaulted 
filters  or  with  open  filters  in  a  warmer  climate. 


2O  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


CHAPTER    III. 

FILTERING  MATERIALS. 
SAND. 

THE  sand  used  for  filtration  may  be  obtained  from  the  sea- 
shore,  from  river-beds  or  from  sand-banks.  It  consists  mainly 
of  sharp  quartz  grains,  but  may  also  contain  hard  silicates.  As 
it  occurs  in  nature  it  is  frequently  mixed  with  clayey  or  other 
fine  particles,  which  must  be  removed  from  it  by  washing  before 
it  is  used.  Some  of  the  New  England  sands,  however,  as  that 
used  for  the  Lawrence  City  filter,  are  so  clean  that  washing 
would  be  superfluous. 

The  grain  size  of  the  sand  best  adapted  to  filtration  has  been 
variously  stated  at  from  \  to  i  mm.,  or  from  0.013  to  0.040  inch. 
The  variations  in  the  figures,  however,  are  due  more  to  the  way 
that  the  same  sand  appears  to  different  observers  than  to  actual 
variations  in  the  size  of  sands  used,  which  are  but  a  small  fraction 
•of  those  indicated  by  these  figures. 

As  a  result  of  experiments  made  at  the  Lawrence  Experi- 
ment Station  *  we  have  a  standard  by  which  we  can  definitely 
compare  various  sands.  The  size  of  a  sand-grain  is  uniformly 
taken  as  the  diameter  of  a  sphere  of  equal  volume,  regardless 
of  its  shape.  As  a  result  of  numerous  measurements  of  grains 
•of  Lawrence  sands,  it  is  found  that  when  the  diameter,  as 
given  above,  is  i,  the  three  axes  of  the  grain,  selecting  the  longest 
possible  and  taking  the  other  two  at  right  angles  to  it,  are,  on  an 
average,  1.38,  1.05,  and  0.69,  respectively  and  the  mean  diameter 
is  equal  to  the  cube  root  of  their  product. 

*Rept.  Mass.  State  Board  of  Health,  1892,  p.  541.     See  Appendix  III. 


FILTERING    MATERIALS. 


21 


It  was  also  found  that  in  mixed  materials  containing  particles 
of  various  sizes  the  water  is  forced  to  go  around  the  larger 
particles  and  through  the  finer  portions  which  occupy  the  inter- 
vening spaces,  so  that  it  is  the  finest  portion  which  mainly  deter- 
mines the  character  of  the  sand  for  filtration.  As  a  provisional 
basis  which  best  accounts  for  the  known  facts,  the  size  of  grain 
such  that  10  per  cent  by  weight  of  the  particles  are  smaller  and 
90  per  cent  larger  than  itself,  is  considered  to  be  the  effective  size. 
The  size  so  calculated  is  uniformly  referred  to  in  speaking  of  the 
size  of  grain  in  this  work. 


Overflow 


FIG.  3. — APPARATUS  USED  FOR  MEASURING  THE  FRICTION  OF  WATER  IN  SANDS. 

Another  important  point  in  regard  to  a  material  is  its  degree 
of  uniformity — whether  the  particles  are  mainly  of  the  same 
size  or  whether  there  is  a  great  range  in  their  diameters.  This 
is  shown  by  the  uniformity  coefficient,  a  term  used  to  designate 
the  ratio  of  the  size  of  grain  which  has  60  per  cent  of  the  sample 
finer  than  itself  to  the  size  which  has  10  per  cent  finer  than, 
itself. 


22 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES, 


The  frictional  resistance  of  sand  to  water  when  closely  packed, 
with  the  pores  completely  filled  with  water  and  in  the  entire 
absence  of  clogging,  was  found  to  be  expressed  by  the  formula 


kit  Fah. 


where  v  is  the  velocity  of  the  water  in  meters  daily  in  a  solid 
column   of  the   same   area    as   that   of  the  sand,  or 
approximately  in  million  gallons  per  acre  daily ; 
c  is  an  approximately  constant  factor; 
d  is  the  effective  size  of  sand  grain  in  millimeters; 
h  is  the  loss  of  head  (Fig.  3) ; 

/is  the  thickness  of  sand  through  which  the  water  passes; 
/  is  the  temperature  (Fahr.). 

TABLE    SHOWING    RATE    AT    WHICH    WATER    WILL    PASS    THROUGH 

EVEN-GRAINED  AND  CLEAN  SANDS  OF  THE  STATED  GRAIN  SIZES 

AND   WITH   VARIOUS   HEADS   AT   A   TEMPERATURE   OF    50°. 


ft 

I 

Effective  Size  in  Millimeters  TO  per  cent  finer  than; 

o.  10 

0.20 

0.30 

0-35 

0.40 

o.  50 

1.  00 

3.00 

.001 

.005 

.010 

.050 

.100 
1.  000 

.01 
.05 
.1  I 

•54 
1.07 
10.70 

.04 

.21 

43 
2.14 

4.28 
42.80 

Million 
.10 
.48 
.96 
4.82 

9.63 
96.30 

Gallons 

•13 

.65 

I-3I 
6.55 
13.10 
I3.I.OO 

per  Acre 

•17 
.85 
I.7I 
8.55 
17.10 
171.00 

daily. 
.27 

1-34 
2.67 
1340 
.  26.70 
267.00 

1.07 

5-35 
10.70 

53-50 
lO/.OO 

963 
48.15 
96.30 

The  above  table  is  computed  with  the  value  c  taken  as  1000, 
this  being  approximately  the  value  deduced  from  the  earliest 
experiments.  More  recent  and  extended  data  have  shown  that 
the  value  of  c  is  not  entirely  constant,  but  depends  upon  the 
uniformity  coefficient,  upon  the  shape  of  the  sand  grains,  upon 
their  chemical  composition,  and  upon  the  cleanness  and  closeness 
of  packing  of  the  sand.  The  value  may  be  as  high  as  1200  for 
very  uniform,  and  perfectly  clean  sand,  and  may  be  as  low  as  400 


FILTERING   MATERIALS.  23 

for  very  closely  packed  sands  containing  a  good  deal  of  alumina  or 
iron,  and  especially  if  they  are  not  quite  clean.  The  friction  is 
usually  less  in  new  sand  than  in  sand  which  has  been  in  use  for 
some  years.  In  making  computations  of  the  frictional  resistance 
of  filters,  the  average  value  of  c  may  be  taken  at  from  700  to  1000 
cor  new  sand,  and  from  500  to  700  for  sand  which  has  been  in  use 
<"or  a  number  of  years. 

The  value  of  <:  decreases  as  the  uniformity  coefficient  increases. 
With  ordinary  filter  sands  with  uniformity  coefficients  of  3  or  less 
the  differences  are  not  great.  With  mixed  sands  having  much 
higher  uniformity  coefficients,  lower  and  less  constant  values  of  c 
are  obtained,  and  the  arrangement  of  the  particles  becomes  a  con- 
trolling factor  in  the  increase  in  friction. 

The  friction  of  the  surface  layer  of  a  filter  is  often  greater  than 
that  of  all  the  sand  below  the  surface.  It  must  be  separately 
computed  and  added  to  the  resistances  computed  by  the  formula, 
as  it  depends  largely  upon  other  conditions  than  those  controlling 
the  resistance  of  the  sand0 

While  the  value  of  c  is  thus  not  entirely  constant,  it  can  be 
estimated  with  approximate  accuracy  for  various  conditions,  from 
a  knowledge  of  the  composition,  condition,  and  cleanliness  of  the 
sand,  and  closeness  of  packing. 

The  following  table  shov/s  the  quantity  of  water  passing  sands 
at  different  temperatures.  This  table  was  computed  with  tempera- 
ture factors  as  given  above,  which  were  based  upon  experiments 
upon  the  flow  of  water  through  sands,  checked  by  the  coefficients 
obtained  from  experiments  with  long  capillary  tubes  entirely  sub- 
merged in  water  of  the  required  temperature. 

RELATIVE    QUANTITIES    OF    WATER    PASSING  AT   DIFFERENT 
TEMPERATURES. 

32°.  ..  .0.70  44°.  ..  .0.90  56°....  1. 10  68°.  ...1.30 

35°.... 0.75  47°.... 0.95  59°.... 1. 15  71°.... i. 35 

38°.  ..  .0.80  50°.  ...i.  oo  62°.  ...1.20  74°.  ...1.40 

41° 0.85  53° 1.05  65° 1.25  77° 1.45 


24  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

The  effect  of  temperature  upon  the  passage  of  water  through 
sands  and  soils  has  been  further  discussed  by  Prof.  L.  G.  Car- 
penter, Engineering  News,  Vol.  XXXIX,  p.  422.  This  article  re- 
views briefly  the  literature  of  the  subject,  and  refers  at  length  to 
the  formula  of  Poiseuille,  published  in  the  Memoires  des  Savants 
Etrangers,  Vol.  XI,  p.  433  (1846).  This  formula,  in  which  the 
quantity  of  water  passing  at  0.0°  Cent.,  is  taken  as  unity,  is  as 
follows : 

Temperature  factor  =  I  +  0.033679^  -f-  0.00022  i/a. 

The  results  obtained  by  this  formula  agree  very  closely  with  those 
given  in  the  above  table  throughout  the  temperature  range  for 
which  computations  are  most  frequently  required.  At  the  higher 
and  lower  temperatures  the  divergencies  are  greater,  as  is  shown  in 
a  communication  in  the  Engineering  News,  Vol.  XL,  p.  26. 

The  quantity  of  water  passing  at  a  temperature  of  50°  Fahr.  is 
in  many  respects  more  convenient  as  a  standard  than  the  quantity 
passing  at  the  freezing-point.  Near  the  freezing-point,  owing  to 
molecular  changes  in  the  water,  the  changes  in  its  action  are  rapid, 
and  the  results  are  less  certain,  and  also  50°  Fahr.  is  a  much  more 
convenient  temperature  for  precise  experiments  than  is  the  freezing 
point. 

SANDS    USED   IN   EUROPEAN   FILTERS. 

To  secure  definite  information  in  regard  to  the  qualities  of  the 
sands  actually  used  in  filtration,  a  large  number  of  European  works 
were  visited  in  1894,  and  samples  of  sand  were  collected  for  anal- 
ysis. These  samples  were  examined  at  the  Lawrence  Experiment 
Station  by  Mr.  H.  W.  Clark,  the  author's  method  of  analysis 
described  in  Appendix  III  being  used.  In  the  following  table, 
for  the  sake  of  compactness,  only  the  leading  points  of  the  analyses, 
namely,  effective  size,  uniformity  coefficient,  and  albuminoid  am- 
monia, are  given.  On  page  28  full  analyses  of  some  samples  from 
a  few  of  the  leading  works  are  given. 


FILTERING   MATERIALS. 
ANALYSES   OF  SANDS   USED   IN   WATER   FILTRATION. 


Source. 

Effective 
Size;  10% 
Finer 
than 
(Milli- 
meters). 

Uni- 
formity 
Coeffi- 
cient. 

Albu- 
minoid 
Ammo- 
nia. 
Parts  in 
ioo,  ooo. 

Remarks. 

London,  E.  London  Co. 
«                      *< 

"         Grand  June... 

Southw'k&V. 
"       Lambeth 

0.44 
0.39 
0.37 
0.26 
0.40 
0.41 
0.38 
0.30 
o  36 

1.8 
2.1 
2.0 
1.9 

3-5 

3-7 
3-5 
1.8 

2.3 

0.45 
26.20 
8.60 
1.90 

10.00 

2.70 
5.00 
2.80 
2.60 

New  sand,  never  used  or  washed. 
Dirty  sand,  very  old. 
Same,  washed  by  hand. 
Sand  from  rough  filter. 
Old  sand  in  final  filter. 
Freshly  washed  old  sand. 

Freshly  washed  new  sand. 
Freshly  washed  old  sand. 

/• 
o  36 

2.4 

0.35 

New  unused  sand,  washed. 

i. 

o  25 

1.7 

0.70 

New  extremely  fine  sand. 

"       Chelsea 

•   2 
0.36 

2.4 

2.10 

Freshly  washed  old  sand. 

Middlesborough  

0.42 

.6 

17.60 

Dirty  sand,  ordinary  scraping. 

0.43 

.6 

7.30 

Same,  after  washing. 

Birmingham  

0.29 

.9 

33-20 

Dirty  sand. 

0.29 

.9 

7  .20 

Sand  below  surface  of  filter. 

Reading        

o  30 

2.  5 

4.00 

Dirtv  sand. 

O   22 

2.O 

1  .50 

Same,  after  washing. 

Antwerp  

o  38 

.6 

7.80 

Dirtv  sand. 

O    3Q 

6 

3  4° 

Same,  after  washing. 

Hamburg 

J7 

o  28 

2  <; 

8  50 

Dirty  sand. 

O   31 

2    3 

o  80 

Same,  after  washing. 

H 

O  34 

2    2 

7.QO 

Dirty  sand,  another  sample. 

U 

o  30 

2   O 

0.90 

Same,  after  washing  drums. 

H 

o  34 

2.3 

1.50 

"           "        ejectors. 

Altona 

O    ^2 

2   O 

Q   OO 

Dirty  sand,  old  filters. 

O   37 

2   O 

I     CO 

Same,  after  washing. 

.1 

O  33 

2   8 

o  co 

Washed  sand  for  new  filters. 

Berlin,  Stralau  

O    33 

0 

12.20 

Dirty  sand-pile. 

o  ^c; 

7 

4    CO 

Filter  No.  6,  3"  below  surface. 

«. 

O   34 

7 

*f-  5^ 
6  30 

"     7   "      " 

.< 

o  3; 

7 

4.00 

"     10    " 

Tegel 

o  18 

6 

I  I    OO 

Dirty  sand,  old  filters. 

•*•  3" 

o  18 

c 

2   80 

Same,  after  washing,  old  filters. 

« 

o  35 

6 

3  2O 

new    " 

"       Miiggfel.  . 

o  3«; 

8 

o  80 

Sand  from  filters  below  surface. 

o  33 

2    O 

6.30 

Dirty  sand,  ordinary  scraping. 

<i 

o.  34 

2.0 

15.30 

"         "       another  sample. 

Charlottenburg  

o  4.0 

2    3 

7  20 

,<                « 

Chemnitz  

o  3; 

2   6 

O.2O 

New  sand  not  yet  used. 

Magdeburg  

o  30 

2    0 

9.  ?o 

Dirty  sand. 

O  4.O 

2   O 

2    80 

Same,  after  washing. 

Breslau   

o  30 

I    8 

I  40 

Normal  new  sand. 

Budapest  

o  20 

2.O 

0.80 

New  washed  Danube  sand. 

o  28 

3    2 

6  20 

Dirty  sand. 

o  30 

3    r 

I     CO 

Same,  after  washing. 

Hague  

O.  IQ 

1.6 

0.70 

Dune-sand  used  for  filtration. 

26  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

ANALYSES   OF   SANDS   USED   IN   WATER  FILTRATION. — Continued. 


Source. 

Effective 
Size;  io# 
Finer 
than 
(Milli- 
meters). 

Uni- 
formity 
Coeffi- 
cient. 

Albu- 
minoid 
Ammo- 
nia. 
Parts  in 

100,000. 

Remarks. 

Schiedam  

0.18 

1.6 

5.60 

Dune-sand    used    for    filtration  • 

O.  •}! 

1.5 

13.  co 

dirty. 
River-sand  ;  dirty. 

Amsterdam  

O.I7 

1.6 

2.4O 

Dune-sand. 

Rotterdam  

O   34 

I    c 

2    3O 

River-sand  •  new 

Liverpool,  Rivington.. 
"        Owesty        .  . 

0.43 
0.32 

o.43 
o  30 

2.0 

2-5 

2.7 

2   6 

0.76 
I.OO 

4.10 

940 

Sand  from  bottom  of  filter. 
New    sand    unwashed    and    un- 
screened. 
Washed  sand  which  has  been  in 
use  30  to  40  years. 
Dirty  sand 

o  31 

4  7 

2    2O 

Same  after  washing 

NOTE. — It  is  obvious  that  in  case  the  sands  used  at  any  place  are  not  always  of  the 
same  character,  as  is  shown  to  be  the  case  by  different  samples  from  some  of  the  works, 
the  examination  of  such  a  limited  number  of  samples  as  the  above  from  each  place  is 
entirely  inadequate  to  establish  accurately  the  sizes  of  sand  used  at  that  particular 
place,  or  to  allow  close  comparisons  between  the  different  works,  and  for  this  reason  no 
such  comparisons  will  be  made.  The  object  of  these  investigations  was  to  determine 
the  sizes  of  the  sands  commonly  used  in  Europe,  and,  considering  the  number  and 
character  of  the  different  works  represented,  it  is  believed  that  the  results  are  ample 
for  this  purpose. 

The  English  and  most  of  the  German  sands  are  washed, 
even  when  entirely  new,  before  being  used,  to  remove  fine 
particles.  At  Breslau,  however,  sand  dredged  from  the  river 
Oder  is  used  in  its  natural  state,  and  new  sand  is  used  for 
replacing  that  removed  by  scraping.  At  Budapest,  Danube  sand 
is  used  in  the  same  way,  but  with  a  very  crude  washing,  and 
it  is  said  that  only  new  unwashed  sand  is  used  at  Warsaw. 

In  Holland,  so  far  as  I  learned,  no  sand  is  washed,  but  new 
sand  is  always  used  for  refilling.  At  most  of  the  works  visited 
dune-sand  with  an  effective  size  of  only  0.17  to  0.19  mm.  is  used, 
and  this  is  the  finest  sand  which  I  have  ever  found  used  for  water 
filtration  on  a  large  scale.  It  should  be  said,  however,  that  the 
waters  filtered  through  these  fine  sands  are  fairly  clear  before 


.    FILTERING    MATERIALS.  2  7 

filtration,  and  are  not  comparable  to  the  turbid  river-waters  often 
filtered  elsewhere,  and  their  tendency  to  choke  the  filters  is  con- 
sequently much  less.  At  Rotterdam  and  Schiedam,  where  the 
raw  water  is  drawn  from  the  Maas,  as  the  principal  stream  of  the 
Rhine  is  called  in  Holland,  river-sand  of  much  larger  grain  size 
is  employed.  It  is  obtained  by  dredging  in  the  river  and  is  never 
washed,  new  sand  always  being  employed  for  refilling. 

The  average  results  of  the  complete  analyses  of  sands  from 
ten  leading  works  are  shown  in  the  table  on  page  28.  These 
figures  are  the  average  of  all  the  analyses  for  the  respective 
places,  except  that  one  sample  from  the  Lambeth  Co.,  which  was 
not  a  representative  one,  was  omitted. 

The  London  companies  were  selected  for  this  comparison 
both  on  account  of  their  long  and  favorable  records  in  filtering 
the  polluted  waters  of  the  Thames  and  Lea,  and  because  they  are 
subject  to  close  inspection ;  and  there  is  ample  evidence  that  the 
filtration  obtained  is  good — evidence  which  is  often  lacking  in  the 
smaller  and  less  closely  watched  works.  For  the  German  works 
Altona  was  selected  because  of  its  escape  from  cholera  in  1892, 
due  to  the  efficient  action  of  its  filters,  and  Stralau  because  of  its 
long  and  favorable  record  when  filtering  the  much-polluted  Spree 
water.  These  two  works  also  have  perhaps  contributed  more 
to  the  modern  theories  of  filtration  than  all  the  other  works  in 
existence.  The  remaining  works  are  included  because  they  are 
comparatively  new,  and  have  been  constructed  with  the  greatest 
care  and  attention  to  details  throughout,  and  the  results  obtained 
are  most  carefully  recorded. 

Some  of  the  most  interesting  of  these  results  are  shown 
graphically  on  page  29.  The  method  of  plotting  is  that  described 
in  Appendix  III. 


28 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


TABLE    SHOWING  THE   AVERAGE   PER   CENT   OF    THE  GRAINS   FINER 
THAN  VARIOUS   SIZES   IN   SANDS   FROM   LEADING  WORKS. 


Per  Cent  by  Weight  Finer  than 

0.106 
mm. 

0.186 
mm. 

0.316 
mm. 

0.46 

mm. 

°-93 
mm. 

2.04 

mm. 

3  89 
mm. 

5.89 

mm. 

O.2 
O 

0 
0 
0.2 
O.I 

0.5 
0.2 

0.7 

0.5 

O.I 

i.5 
i  .1 

0.3 

0.2 
0-5 

3.6 

3-1 
8.0 

5-5 
5.o 
10.9 

7.8 
7.0 
4-5 
7.9 

22.2 
17.4 

34-1 
26.6 
28.6 
33-2 
28.7 

37-3 

35i 

33.6 

69.7 

47-1 
69.7 
63.0 
63.0 

74-4 
72.1 
86.9 
94-3 
79-7 

89.8 

68.2 

83.5 
79-2 
76.7 
95.7 
92.1 
95-4 
98.5 
94-3 

95.0 

84.7 
90.0 

88.0 
86.0 

99-5 
95.8 
97.6 
99.1 
98.5 

99-0 

93-6 

94.0 
94-3 
93-6 

Southwark  and  Vauxhall  . 
Lambeth  

Chelsea                   

Tegel  

O.I 

Average  of  all 

0.06 

0.56 

6.33 

29.71 

7L99 

87.34 

93-42 

(9745) 

AVERAGE  EFFECTIVE   SIZE,   UNIFORMITY   COEFFICIENT,   AND  ALBU- 
MINOID AMMONIA  IN   SANDS   FROM   TEN   LEADING  WORKS. 

I.      LONDON   FILTERS. 


Effective 
Size;  10% 

Uniformity 

Albuminoic 

1  Ammonia. 

Finer  than 
(Millimeters). 

Coefficient 

Dirty  Sand. 

Washed  Sand. 

East  London  

o  40 

2.O 

26  oo 

8  60 

Grand  Junction  

O.4O 

3.6 

IO.OO 

2.70 

Southwark  and  Vauxhall  

O    34. 

2    C 

30O 

•^7 
o  36 

2  4. 

2   60 

Chelsea  

o  36 

2.4 

2.  IO 

O    V7 

2   6 

18  oo 

3   Q8 

II.      GERMAN   WORKS. 


o  34 

1.7 

1  2.  2O 

4.  OO 

Teeel 

O  37 

i  6 

1  1    OO 

•3     OO 

Mii  creel   . 

o  34 

2   O 

10   80 

o  80 

o  34 

2.  3 

Q   OO 

I     SO 

o  31 

2    3 

8    20 

I    O7 

Average    

o.  14 

2.O 

IO    25 

2    O7 

r 


FIL  TERING    MA  TERIA  LS. 


29 


The  averages  show  the  effective  size  of  the  English  sands  to  be 
slightly  greater  than  that  of  the  German  sands — 0.37  instead  of 
0.34  mm. — but  the  difference  is  very  small.  The  entire  range  for 


Locality 


Description 


Mechanical  Analysis 
Fittering  Material. 

dllen  Hazen 
Consulting  Engineer. 


Effective  Size -nun. .... 


Uniformity  Coefficient. .. 

Limt:HC/test. 

Dust 


Diameters  in  millimeters. 

FIG.  sa.— SAND  ANALYSIS  SHEET,  WITH  ANALYSES  OF  SEVERAL  EUROPEAN 

FILTER  SANDS. 

the  ten  works  is  only  from  0.31  to  0.40  mm.,  and  these  may  be 
taken  as  the  ordinary  limits  of  effective  size  of  the  sands  em- 
ployed in  the  best  European  works.  The  average  for  the  other 
sixteen  works  given  above,  including  dune-sands,  is  0.31  mm.,  or, 
omitting  the  dune-sands,  0.34  mm. 

It  is  important  that  filter  sands  should  be  free  from  lime. 
When  water  is  filtered  through  such  sands,  no  increase  in  hardness 
results.  When,  however,  water  is  filtered  through  sand  containing 


30  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

lime,  some  of  it  is  usually  dissolved  and  the  water  is  made  harder. 
The  amount  of  lime  taken  up  in  this  way  depends  both  upon  the 
character  of  the  sand,  and  upon  the  solvent  power  of  the  water; 
and  it  does  not  necessarily  follow  that  a  sand  containing  lime 
cannot  be  used  for  filtration,  but  a  sand  nearly  free  from  lime  is 
to  be  preferred. 

The  presence  of  lime  in  sand  can  usually  be  detected  by 
moistening  it  with  hydrochloric  acid.  The  evolution  of  gas  shows 
the  presence  of  lime.  Some  idea  of  the  amount  of  lime  can  be 
obtained  from  the  amount  of  gas  given  off,  and  the  appearance  of 
the  sample  after  the  treatment,  but  chemical  analysis  is  necessary 
to  determine  correctly  the  amount. 

Experiments  with  filters  at  Pittsburg  were  made  with  sand 
containing  1.3  per  cent  of  lime,  the  result  being  that  the 
hardness  of  the  water  was  increased  about  one  part  in 
100,000;  but  the  amount  of  lime  in  the  sand  was  so  small  that 
it  would  be  washed  out  after  a  time,  and  then  the  harden- 
ing effect  would  cease.  Larger  amounts  of  lime  would  continue 
their  action  for  a  number  of  years  and  would  be  more  objection- 
able. 

Turning  to  the  circumstances  which  influence  the  selection  of 
the  sand  size,  we  find  that  both  the  quality  of  the  effluent  obtained 
by  filtration  and  the  cost  of  filtration  depend  upon  the  size  of  the 
sand-grains. 

With  a  fine  sand  the  sediment  layer  forms  more  quickly  and 
the  removal  of  bacteria  is  more  complete,  but,  on  the  other  hand, 
the  filter  clogs  quicker  and  the  dirty  sand  is  more  difficult  to  wash, 
so  that  the  expense  is  increased. 

EFFECT   OF    SIZE   OF   GRAIN    UPON   EFFICIENCY   OF   FILTRATION. 

It  is  frequently  stated  that  it  is  only  the  sediment  layer  which 
performs  the  work  of  filtration,  and  that  the  sand  which  sup- 
ports it  plays  hardly  a  larger  part  than  does  the  gravel  which 


FILTERING   MATERIALS.  31 

carries  the  sand,  and  under  some  circumstances  this  is  un- 
doubtedly the  case.  Nevertheless  sand  in  itself,  without  any 
sediment  layer,  especially  when  not  too  coarse  and  not  in  too 
thin  layers,  has  very  great  purifying  powers,  and,  in  addition, 
acts  as  a  safeguard  by  positively  preventing  excessive  rates  of 
filtration  on  account  of  its  frictional  resistance.  As  an  illustration 
take  the  case  of  a  filter  of  sand  with  an  effective  size  of  0.35  mm. 
and  the  minimum  thickness  of  sand  allowed  by  the  German  Board 
of  Health,  namely,  one  foot,  and  let  us  suppose  that  with  clogging 
the  loss  of  head  has  reached  two  feet  to  produce  the  desired  veloc- 
ity of  2.57  million  gallons  per  acre  daily.  Suppose  now  that  by 
some  accident  the  sediment  layer  is  suddenly  broken  or  removed 
from  a  small  area,  the  water  will  rush  through  this  area,  until  a 
new  sediment  layer  is  formed,  at  a  rate  corresponding  to  the  size, 
pressure,  and  depth  of  the  sand,  or  260  million  gallons  per  acre 
daily — a  hundred  times  the  standard  rate.  Under  these  condi- 
tions the  passing  water  will  not  be  purified,  but  will  pollute  the 
entire  effluent  from  the  filter.  Under  corresponding  conditions,, 
with  a  deep  filter  of  fine  sand,  say  with  an  effective  size  of  0.20 
mm.  and  5  feet  deep,  the  resulting  rate  would  be  only  17  million 
gallons  per  acre  daily,  or  less  than  seven  times  the  normal,  and 
v-Tith  the  water  passing  through  the  full  depth  of  fine  sand,  the 
resulting  deterioration  in  the  effluent  before  the  sand  again  be- 
came so  clogged  as  to  reduce  the  rate  to  nearly  the  normal, 
would  be  hardly  appreciable. 

The  results  at  Lawrence  have  shown  that  with  very  fine  sands 
0.09  and  0.14  mm.,  and  4  to  5  feet  deep,  with  the  quantity  of  water 
which  can  practically  be  made  to  pass  through  them,  it  is  almost 
impossible  to  drive  more  than  an  insignificant  fraction  of  the 
bacteria  into  the  effluent.  Even  when  the  sands  are  entirely 
new,  or  have  been  scraped  or  disturbed  in  the  most  violent  way, 
the  first  effluent  passing,  before  the  sediment  layer  could  have 
beea  formed,  is  of  good  quality.  Still  finer  materials,  0.04  to 
006  mm.,  as  far  as  could  be  determined,  secured  the  absolute 


32  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

removal  of  all  bacteria,  but  the  rates  of  filtration  which  were 
possible  were  so  low  as  to  preclude  their  practical  application. 

With  coarser  sands,  as  long  as  the  filter  is  kept  at  a  steady 
rate  of  filtration,  without  interruptions  of  any  kind,  entirely  satis- 
factory results  are  often  obtained,  although  never  quite  so  good 
as  with  the  finer  sands.  Thus  at  Lawrence  the  percentages  of 
bacteria  (B.  prodigiosns)  appearing  in  the  effluents  under  compar- 
able conditions  were  as  follows : 

1892          1893 

With  effective  grain  size  0.38  mm o.  16 

"  "       "     0.29    "    0.16 

"  "       "     0.26    "    o.io 

"  "       "     0.20    "    0.13  o.oi 

"  "       "     0.14    "    0.04  0.03 

"     0.09    "    0.02  0.02 

We  may  thus  conclude  that  fine  sands  give  normally  some- 
what better  effluents  than  coarser  ones,  and  that  they  are  much 
more  likely  to  give  at  least  a  tolerably  good  purification  under 
unusual  or  improper  conditions. 

EFFECT   OF   GRAIN   SIZE   UPON   FREQUENCY   OF   SCRAPING. 

The  practical  objection  to  the  use  of  fine  sand  is  that  it 
becomes  rapidly  clogged,  so  that  filters  require  to  be  scraped  at 
shorter  intervals,  and  the  sand  washing  is  much  more  difficult 
and  expensive.  The  quantities  of  water  filtered  between  succes- 
sive scrapings  at  Lawrence  in  millions  of  gallons  per  acre  under 
comparable  conditions  have  been  as  follows: 

1892        1893 

Effective  size  of  sand  grain  0.38  mm... , 79 

"          "     "      "         "       0.29  mm 70 

"          "     "      "         "       o.26mm 57 

"     "      "         "       0.20  mm 58        

"     "      "         "       0.14  mm 45         49 

"     "      "        "       o.09mm 24        14 


FILTERING   MATERIALS.  33 

The  increase  in  the  quantities  passed  between  scrapings  with 
increasing  grain  size  is  very  marked. 

With  the  fine  sands,  the  depth  to  which  the  sand  becomes 
dirty  is  much  less  than  with  the  coarse  sands,  but  as  it  is  not 
generally  practicable  to  remove  a  layer  of  sand  less  than  about 
0.6  inch  thick,  even  when  the  actual  clogged  layer  is  thinner 
than  this,  the  full  quantity  of  sand  has  to  be  removed ;  and 
the  quantities  of  sand  to  be  removed  and  washed  are  inverse- 
ly proportional  to  the  quantities  of  water  filtered  between 
scrapings.  On  the  other  hand,  with  very  coarse  sands  the 
sediment  penetrates  the  sand  to  a  greater  depth  than  the  0.6 
inch  necessarily  removed,  so  that  a  thicker  layer  of  sand  has  to 
be  removed,  which  may  more  than  offset  the  longer  interval. 
This  happens  occasionally  in  water-works,  and  a  sand  coarse 
enough  to  allow  it  occur  is  always  disliked  by  superintendents, 
and  is  replaced  with  finer  sand  as  soon  as  possible.  It  is  ob- 
vious that  the  minimum  expense  for  cleaning  will  be  secured 
with  a  sand  which  just  does  not  allow  this  deep  penetration,  and 
I  am  inclined  to  think  that  the  sizes  of  the  sands  in  use  have  actu- 
ally been  determined  more  often  than  otherwise  in  this  way,  and 
that  the  coarsest  samples  found,  having  effective  sizes  of  about 
0.40  mm.,  represent  the  practical  limit  to  the  coarseness  of  the 
sand,  and  that  any  increase  above  this  size  would  be  followed 
by  increased  expense  for  cleaning  as  well  as  by  decreased 
efficiency. 

SELECTION   OF   SAND. 

In  selecting  a  sand  for  filtration,  when  it  is  considered  that 
repeated  washings  will  remove  some  of  the  finest  particles,  and 
so  increase  slightly  the  effective  size,  a  new  sand  coarser  than 
0.35  mm.  would  hardly  be  selected.  Perhaps  0.20  might  be 
given  as  a  suitable  lower  limit.  For  comparatively  clear  lake-  or 
reservoir-waters  a  finer  sand  could  probably  be  used  than  would 
be  the  case  with  a  turbid  river-water.  A  mixed  sand  having  a 


34  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

uniformity  coefficient  above  3.0  would  be  difficult  to  wash  without 
separating  it  into  portions  of  different  sizes,  and,  in  general,  the 
lower  the  coefficient,  that  is,  the  more  uniform  the  grain  sizes,  the 
better.  Great  pains  should  be  taken  to  have  the  sand  of  the 
same  quality  throughout,  especially  in  the  same  filter,  as  any 
variations  in  the  grain  sizes  would  lead  to  important  variations 
in  the  velocity  of  filtration,  the  coarser  sands  passing  more  than 
their  share  of  water  (in  proportion  to  the  square  of  the  effective 
sizes)  and  with  reduced  efficiency. 

At  Lawrence  a  sufficient  quantity  of  natural  sand  was  found 
of  the  grade  required  ;  but  where  suitable  material  cannot  be  so 
obtained  it  is  necessary  to  use  other  methods.  A  mixed  mate- 
rial can  be  screened  from  particles  which  are  too  large,  and  can 
be  washed  to  free  it  from  its  finer  portions,  and  in  this  way  a 
good  sand  can  be  prepared,  if  necessary,  from  what  might  seem 
to  be  quite  unpromising  material.  The  methods  of  sand-wash- 
ing will  be  described  in  Chapter  V. 

THICKNESS   OF  THE   SAND   LAYER. 

The  thickness  of  the  sand  layer  is  made  so  great  that  when 
it  is  repeatedly  scraped  in  cleaning  the  sand  will  not  become  too 
thin  for  good  filtration  for  a  considerable  time.  When  this 
occurs  the  removed  sand  must  be  replaced  with  clean  sand.  The 
original  thickness  of  the  sand  in  European  filters  is  usually  from 
24  to  48  inches,  thicknesses  between  30  and  40  inches  being  ex- 
tremely common,  and  this  is  reduced  before  refilling  to  from  12 
to  24  inches.  The  Imperial  Board  of  Health  of  Germany  has 
fixed  12  inches  as  a  limit  below  which  the  sand  should  never 
be  scraped,  and  a  higher  limit  is  recommended  wherever  pos- 
sible. 

A  thick  sand  layer  has  the  same  steadying  action  as  a  fine 
sand,  and  tends  to  prevent  irregularities  in  the  rate  of  filtration 
in  proportion  to  its  frictional  resistance,  and  that  without  in- 
creasing the  frequency  of  cleaning;  but,  on  the  other  hand,  it  in- 


FILTERING   MATERIALS.  35 

creases  the  necessary  height  of  the  filter,  throughout,  and  conse- 
quently the  cost  of  construction. 

In  addition  to  the  steadying  effect  of  a  deep  sand  layer,  some 
purification  takes  place  in  the  lower  part  of  the  sand  even  with 
a  good  sediment  layer  on  the  surface,  and  the  efficiency  of  deep 
filters  is  greater  than  that  of  shallow  ones. 

Layers  of  finer  materials,  as  fine  sand  or  loam,  in  the  lower 
part  of  a  filter,  which  would  otherwise  give  increased  efficiency 
without  increasing  the  operating  expenses,  cannot  be  used. 
Their  presence  invariably  gives  rise  sooner  or  later  to  sub-sur- 
face clogging  at  the  point  of  junction  with  the  coarser  sand,  as- 
has  been  found  by  repeated  tests  at  Lawrence  as  well  as  in  some 
of  the  Dutch  filters  where  such  layers  were  tried ;  and  as  there 
is  no  object  in  putting  a  coarser  sand  under  a  finer,  the  filter  sand 
is  best  all  of  the  same  size  and  quality  from  top  to  bottom. 

UNDERDRAINING. 

The  underdrains  of  a  filter  are  simply  useful  for  collecting 
the  filtered  water ;  they  play  no  part  in  the  purification.  One  of 
the  first  requirements  of  successful  filtration  is  that  the  rate  of 
filtration  shall  be  practically  the  same  in  all  parts  of  the  filter. 
This  is  most  difficult  to  secure  when  the  filter  has  just  been 
cleaned  and  the  friction  of  the  sand  layer  is  at  a  minimum.  If 
the  friction  of  the  water  in  entering  and  passing  through  the 
underdrains  is  considerable,  the  more  remote  parts  of  the  filters 
will  work  under  less  pressure,  and  will  thus  do  less  than  their 
share  of  the  work,  while  the  parts  near  the  outlet  will  be  over- 
taxed, and  filtering  at  too  high  rates  will  yield  poor  effluents. 

To  avoid  this  condition  the  underdrains  must  have  such  a 
capacity  that  their  frictional  resistance  will  be  only  a  small  frac- 
tion of  the  friction  in  the  sand  itself  just  after  cleaning. 

GRAVEL   LAYERS. 

The  early  filters  contained  an  enormous  quantity  of  gravel, 
but  the  quantity  has  been  steadily  reduced  in  successive  plants. 


36  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

Thus  in  1866  Kirkwood,  as  a  result  of  his  observations,  recom- 
mended the  use  of  a  layer  four  feet  thick,  and  in  addition  a  foot 
of  coarse  sand,  while  at  the  present  time  new  filters  rarely  have 
more  than  two  feet  of  gravel.  Even  this  quantity  seems  quite 
superfluous,  when  calculations  of  itsfrictional  resistance  are  made. 
Thus  a  layer  of  gravel  with  an  effective  size  of  20  mm.*  (which  is 
much  finer  than  that  generally  employed)  only  6  inches  thick  will 
carry  the  effluent  from  a  filter  working  at  a  rate  of  2.57  million 
gallons  per  acre  daily  for  a  distance  of  8  feet  (that  is,  with  under- 
drains  16  feet  apart),  with  a  loss  of  head  of  only  o.ooi  foot,  and 
for  longer  distances  tile  drains  are  cheaper  than  gravel.  To  pre- 
vent the  sand  from  sinking  into  the  coarse  gravel,  intermediate 
sizes  of  gravel  must  be  placed  between,  each  grade  being  coarse 
enough  so  that  there  is  no  possibility  of  its  sinking  into  the  layer 
below.  The  necessary  thickness  of  these  intermediate  layers  is 
very  small,  the  principal  point  being  to  have  a  layer  of  each  grade 
at  every  point.  Thus  on  the  6  inches  of  20  mrn.  gravel  men- 
tioned above,  three  layers  of  two  inches  each,  of  8  and  3  mm. 
gravel  and  coarse  sand,  with  a  total  height  of  six  inches,  or  other 
corresponding  and  convenient  depths  and  sizes,  would,  if  carefully 
placed,  as  effectually  prevent  the  sinking  of  the  filter  sand  into 
the  coarse  gravel  as  the  much  thicker  layers  used  in  the  older 
plants. 

The  gravel  around  the  drains  should  receive  special  attention. 
Larger  stones  can  be  here  used  with  advantage,  taking  care  that 
adequate  spaces  are  left  for  the  entrance  of  the  water  into  the 
drains  at  a  low  velocity,  and  to  make  everything  so  solid  in  this 
neighborhood  that  there  will  be  no  chance  for  the  stones  to 
settle  which  might  allow  the  sand  to  reach  the  drains. 

At  the  Lawrence  filter,  at  Konigsberg  in  Prussia,  at  Amster- 
dam and  other  places,  the  quantity  of  gravel  is  reduced  by  put- 
ting the  drains  in  trenches,  so  that  the  gravel  is  reduced  from 

*  The  method  of  calculating  the  size  is  given  in  Appendix  III. 


RECONSTRUCTING  THE  UNDERDRAINAGE  SYSTEM  OF  A 
FILTER  AFTER  25  YEARS  OF  USE,  BREMEN. 


IDLACING  SAND  IN  A  FILTER,  CHOISY  LE  Roi  (PARIS). 

[To  face  page  36.] 


OF   THB 

UNIVERSITY 
^ 


FILTERING   MATERIALS.  37 

a  maximum  thickness  at  the  drain  to  nothing  half  way  between 
drains.  The  economy  of  the  arrangement,  however,  as  far  as 
friction  is  concerned  is  not  so  great  as  would  appear  at  first  sight, 
and  the  cost  of  the  bottom  may  be  increased  ;  but  on  the  other 
hand  it  gives  a  greater  depth  of  gravel  for  covering  the  drains 
with  a  small  total  amount  of  gravel. 

As  even  a  very  small  percentage  of  fine  material  is  capa- 
ble of  getting  in  the  narrow  places  and  reducing  the  carrying 
power  of  the  gravel,  it  is  important  that  all  such  matters  should 
be  carefully  removed  by  washing  before  putting  the  gravel  in 
place.  In  England  and  Germany  gravel  is  commonly  screened 
for  use  in  revolving  cylinders  of  wire-cloth  of  the  desired  sizes, 
on  which  water  is  freely  played  from  numerous  jets,  thus  secur- 
ing perfectly  clean  gravel.  In  getting  gravel  for  the  Lawrence 
filter,  an  apparatus  was  used,  in  which  advantage  was  taken  of 
the  natural  slope  of  the  gravel  bank  to  do  the  work,  and  the  use 
of  power  was  avoided.  The  respective  grades  of  gravel  obtained 
were  even  in  size,  and  reasonably  free  from  fine  material,  but  it 
was  deemed  best  to  wash  them  with  a  hose  before  putting  them 
in  the  filter. 

To  calculate  the  frictional  resistance  of  water  in  passing 
gravel,  we  may  assume  that  for  the  very  low  velocities  which 
are  actually  found  in  filters  the  quantity  of  water  passing  varies 
directly  with  the  head,  which  for  these  velocities  is  substantially 
correct^  although  it  would  not  be  true  for  higher  rates,  especially 
with  the  coarser  gravels.*  In  the  case  of  parallel  underdrains  the 
friction  from  the  middle  point  between  drains  to  the  drains  may 
be  calculated  by  the  formula : 

~      ,  ,  i  Rate  of  filtration  X  (i  distance  between  drains)* 

Total  head  =  -  — r—  „   . — L. 

2  Average  depth  of  gravel  X  discharge  coefficient 

The  discharge  coefficient  for  any  gravel  is  1000  times  the  quan- 

*  A  full  table  of  frictions  with  various  velocities  and  gravels  was  given  in  the  Rept. 
of  Mass.  State  Board  of  Health,  1892,  p.  555. 


38  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

tity  of  water  which  will  pass  when  —  is  10100  expressed  in  million 

gallons  per  acre  daily.     The  approximate  values  of  this  coefficient 
for  different-sized  gravels  are  as  follows: 

VALUES   OF   DISCHARGE    COEFFICIENT. 

For  gravel  with  effective  size     5  mm c  =    23,000 

"          "         "             "          "  10  "     c—    65,000 

"           "         "             "          "  15  "     c=  110,000 

"         "            "          «  20  "     c—  160,000 

"         "            "          "  25  "     c  =  230,000 

"  30  "      c=  300,000 

"  35  "     c  =  390,000 

"            "          "  40  "     c  =  480,000 

Example :  What  is  the  loss  of  head  in  the  gravel  at  a  rate  of 
filtration  of  2  million  gallons  per  acre  daily,  with  underdrains  20 
feet  apart,  where  the  supporting  gravel  has  an  effective  size  of  35 
millimeters,  and  is  uniformly  i  ft.  deep  ? 

Total  head  =  -      2  X  IO'      =  .000256  ft. 
2  i  X  390.000 

The  total  friction  would  be  the  same  with  the  same  average 
depth  of  gravel  whether  it  was  uniformly  i  foot  deep,  or  decreas- 
ing from  1.5  at  the  drains  to  0.5  in  the  middle,  or  from  2.0  to  o. 
The  reverse  case  with  the  gravel  layer  thicker  in  the  middle  than 
at  the  drains  does  not  occur  and  need  not  be  discussed. 

The  depth  of  gravel  likely  to  be  adopted  as  a  result  of  this 
calculation,  when  the  drains  are  not  too  far  apart,  will  be  much 
less  than  that  actually  used  in  most  European  works,  but  as  the 
two  feet  or  more  there  employed  are,  I  believe,  simply  the  result 
of  speculation,  there  is  no  reason  for  following  the  precedent 
where  calculations  show  that  a  smaller  quantity  is  adequate. 

The  reason  for  recommending  a  thin  lower  layer  of  coarse 
gravel,  which  alone  is  assumed  to  provide  for  the  lateral  move- 


FILTERING   MATERIALS.  39 

ment  of  the  water,  is  that  if  more  than  about  six  inches  of  gravel 
is  required  to  give  a  satisfactory  resistance,  it  will  almost  always 
be  cheaper  to  use  more  drains  instead  of  more  gravel ;  and  the 
reason  for  recommending  thinner  upper  layers  for  preventing  the 
sand  from  settling  into  the  coarse  gravel  is  that  no  failures  of 
this  portion  of  filters  are  on  record,  and  in  the  few  instances 
where  really  thin  layers  have  been  used  the  results  have  been 
entirely  satisfactory.  In  Konigsberg  filters  were  built  by  Fruh- 
ling,*  in  which  the  sand  was  supported  by  five  layers  of  gravel  of 
increasing  sizes,  respectively  1.2,  1.2,  1.6,  2.0,  3.2,  or,  together,  9.2 
inches  thick,  below  which  there  were  an  average  of  five  inches  of 
coarse  gravel.  These  were  examined  after  eight  years  of  oper- 
ation and  found  to  be  in  perfect  order. 

At  the  Lawrence  Experiment  Station  filters  have  been  re- 
peatedly constructed  with  a  total  depth  of  supporting  gravel 
layers  not  exceeding  six  inches,  and  among  the  scores  of  such 
filters  there  has  not  been  a  single  failure,  and  so  far  as  they  have 
been  dug  up  there  has  never  been  found  to  have  been  any  move- 
ment whatever  of  the  sand  into  the  gravel.  The  Lawrence  city 
filter,  built  with  corresponding  layers,  has  shown  no  signs  of  be- 
ing inadequately  supported.  In  arranging  the  Lawrence  gravel 
layers  care  has  always  been  taken  that  no  material  should  rest 
on  another  material  more  than  three  or  four  times  as  coarse  as 
itself,  and  that  each  layer  should  be  complete  at  every  point,  so 
that  by  no  possibility  could  two  layers  of  greater  difference  in 
size  come  together.  And  it  is  believed  that  if  this  is  carefully 
attended  to,  no  trouble  need  be  anticipated,  however  thin  the 
single  layers  may  be. 

UNDERDRAINS. 

The  most  common  arrangement,  in  other  than  very  small 
filters,  is  to  have  a  main  drain  through  the  middle  of  the  filter, 

*  Friihling,  Handbuch  der  Ingenieurwissenschaften,  II.  Band,  VI.  Kapitel. 


4°  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

with  lateral  drains  at  regular  intervals  from  it  to  the  sides.  The 
sides  of  the  main  drain  are  of  brick,  laid  with  open  joints  to  ad- 
mit water  freely,  and  the  top  is  usually  covered  with  stone  slabs. 
The  lateral  drains  may  be  built  in  the  same  way,  but  tile  drains 
are  also  used  and  are  cheaper.  Care  must  be  taken  with  the  latter 
that  ample  openings  are  left  for  the  admission  of  water  at  very 
low  velocities.  It  is  considered  desirable  to  have  these  drains 
go  no  higher  than  the  top  of  the  coarsest  gravel ;  and  this  will 
often  control  the  depth  of  gravel  used.  If  they  go  higher,  the 
top  must  be  made  tight  to  prevent  the  entrance  of  the  fine 
gravels  or  sand.  Sometimes  they  are  sunk  in  part  or  wholly 
(especially  the  main  drain)  below  the  floor  of  the  filter.  With 
gravel  placed  in  waves,  that  is,  thicker  over  the  drains  than  else- 
where, as  mentioned  above,  the  drains  are  covered  more  easily 
than  with  an  entirely  horizontal  arrangement.  When  this  is  done, 
the  floor  of  the  filter  is  trenched  to  meet  the  varying  thickness 
of  gravel,  so  that  the  top  of  the  latter  is  level,  and  the  sand  has  a 
uniform  thickness. 

Many  filters  (Lambeth,  Brunswick,  etc.)  are  built  with  a 
double  bottom  of  brick,  the  upper  layer  of  which,  with  open  joints, 
supports  the  gravel  and  sand,  and  is  itself  supported  by  numerous 
small  arches  or  other  arrangements  of  brick,  which  serve  to 
carry  the  water  to  the  outlet  without  other  drains.  This  ar- 
rangement allows  the  use  of  a  minimum  quantity  of  gravel,  but  is 
undoubtedly  more  expensive  than  the  usual  form,  with  only  the 
necessary  quantity  of  gravel ;  and  I  am  unable  to  find  that  it  has 
any  corresponding  advantages. 

The  frictional  resistance  of  underdrains  requires  to  be  care- 
fully calculated  ;  and  in  doing  this  quite  different  standards  must 
be  followed  from  those  usually  employed  in  determining  the 
sizes  of  water-pipes,  as  a  total  frictional  resistance  of  only  a  few 
htmdredths  of  a  foot,  including  the  velocity  head,  may  cause 
serious  irregularities  in  the  rate  of  filtration  in  different  parts  of 
the  filter. 


FILTERING   MATERIALS.  41 

The  sizes  of  the  underdrains  differ  very  widely  in  proportion 
to  the  sizes  of  the  filters  in  European  works,  some  of  them  being- 
excessively  large,  while  in  other  cases  they  are  so  small  as  ta 
suggest  a  doubt  as  to  their  allowing  uniform  rates  of  filtration, 
especially  just  after  cleaning. 

I  would  suggest  the  following  rules  as  reasonably  sure  to  lead 
to  satisfactory  results  without  making  an  altogether  too  lavish 
provision :  In  the  absence  of  a  definite  determination  to  run 
filters  at  some  other  rate,  calculate  the  drains  for  the  German 
standard  rate  of  a  daily  column  of  2.40  meters,  equal  to  2.57 
million  gallons  per  acre  daily.  This  will  insure  satisfactory 
work  at  all  lower  rates,  and  no  difficulty  on  account  of  the 
capacity  of  the  underdrains  need  be  then  anticipated  if  the  rate 
is  somewhat  exceeded.  The  area  for  a  certain  distance  from 
the  main  drain  depending  upon  the  gravel  may  be  calculated  as 
draining  directly  into  it,  provided  there  are  suitable  openings, 
and  the  rest  of  the  area  is  supposed  to  drain  to  the  nearest  lateral 
drain. 

In  case  the  laterals  are  round-tile  drains  I  would  suggest  the 
following  limits  to  the  areas  which  they  should  be  allowed  to 
drain : 

e  ~     .  To  Drain  an  Area  not         Corresponding  Velocity  of 

Diameter  of  Dram.  Exceeding  Water  in  Drain. 

4  inches 290  square  feet.  0.30 foot. 

6        "     750  "  0.35     " 

8        "     1530       "         "  0.40     " 

10        "     2780       "         "  0.46     " 

12        "     4400       "         "  0.51     " 

And  for  larger  drains,  including  the  main  drains,  their  cros^- 
sections  at  any  point  should  be  at  least  T7V?r  °f  tne  area  drained, 
giving  a  velocity  of  0.55  foot  per  second  with  the  rate  of 
filtration  mentioned  above. 

The  total  friction  of  the  underdrains  from  the  most  remote 
points  to  the  outlet  will  be  friction  in  the  gravel,  plus  friction  in 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


the  lateral  drains,  plus  the  friction  in  main  drain,  plus  the  veloc- 
ity head. 

I  have  calculated  in  this  way  the  friction  of  one  of  the  Ham- 
burg filters  for  the  rate  of  1,600,000  gallons  per  acre  daily  at 
which  it  is  used.  The  friction  was  calculated  for  each  section 
of  the  drains  separately,  so  that  the  friction  from  intermediate 
points  was  also  known.  Kutter's  formula  was  used  throughout 
with  n  =  0.013.  On  the  accompanying  plan  of  the  filter  I  have 


Iffl 


l 


V 


ft 

'  ? 


v 


Drain 


_ 


>'. 


4 

InlejtWellj 


0  10  20          30          40          50          60  7,0      Meters 

[.nrrpul  ,    ,    ,1,   .    ,  '|    !    |   ,'  i   !    i'i   i    |  '|  t    i    i   i   t 

0  50  100  150  200  250  Feet 

FIG.  4. — PLAN  OF  ONE  OF  THE  HAMBURG  FILTERS,  SHOWING  FRICTIONAL  RESIST- 
ANCE OF  THE  UNDERDRAINS. 

drawn  the  lines  of  equal  frictional  resistance  from  the  junction 
of  the  main  drain  with  the  last  laterals.  My  information  was 
incomplete  in  regard  to  one  or  two  points,  so  that  the  calcula- 
tion may  not  be  strictly  accurate,  but  it  is  nearly  so  and  will 
illustrate  the  principles  involved. 

The  extreme  friction  of  the  underdrains  is  u  millimeters 
=  0.036  foot. 

The  frictional  resistance  of  the  sand  39  inches  thick,  effective 
size  0.32  mm.  and  rate  1.60  million  gallons  per  acre  daily,  when 
absolutely  free  from  clogging,  is  by  the  formula,  page  21,  15 


••*»,;.  3  V< 

_4  \ 


FILTERING   MATERIALS.  43 

mm.,  or  .0490  foot,  when  the  temperature  is  50°.  Practically 
there  is  some  matter  deposited  upon  the  surface  of  the  sand 
before  nitration  starts,  and  further,  after  the  first  scraping,  there 
is  some  slight  clogging  in  the  sand  below  the  layer  removed  by 
scraping.  We  can  thus  safely  take  the  minimum  frictional 
resistance  of  the  sand  including  the  surface  layer  at  .07  foot. 
The  average  friction  of  the  underdrains  for  all  points  is  about 
.023  foot  and  the  friction  at  starting  will  be  .07  +  .023  =  .093 
foot  (including  the  friction  in  the  last  section  to  the  effluent 
well  where  the  head  is  measured,  .100  foot,  but  the  fric- 
tion beyond  the  last  lateral  does  not  affect  the  uniformity  of 
filtration).  The  actual  head  on  the  sand  close  to  the  outlet  will 

be  .003  and  the  rate  of  filtration  -25.  1.60  =  2.12.     The  actual 

.070 

head  at  the  most  remote  point  will  be  .093  —  .036  =  .057,  and  the 
rate  of  filtration  will  there  be  — —  .  160  =  1.30  million  gallons  per 

acre  daily.  The  extreme  rates  of  filtration  are  thus  2.12  and 
1.30,  instead  of  the  average  rate  of  1.60.  As  can  be  seen  from 
the  diagram,  only  very  small  areas  work  at  these  extreme 
rates,  the  great  bulk  of  the  area  working  at  rates  much  nearer 
the  average.  Actually  the  filter  is  started  at  a  rate  below  1.60, 
and  the  nearest  portion  never  filters  so  rapidly  as  2.12,  for  when 
the  rate  is  increased  to  the  standard,  the  sand  has  become  so  far 
clogged  that  the  loss  of  head  is  more  than  the  .07  foot  assumed, 
and  the  differences  in  the  rates  are  correspondingly  reduced. 
Taking  this  into  account,  it  would  not  seem  that  the  irregularities 
in  the  rate  of  filtration  are  sufficient  to  affect  seriously  the  action 
of  the  filter.  They  could  evidently  have  been  largely  reduced 
by  moderately  increasing  the  sizes  of  the  lower  ends  of  the 
underdrains,  where  most  of  the  friction  occurs  with  the  high 
velocities  (up  to  .97  foot)  which  there  result. 

The   underdrains  of   the  Warsaw   filters  were   designed   by 
Lindley  to  have  a  maximum  loss  of  head  of  only  .0164  foot  when 


44  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

filtering  at  a  rate  of  2.57,  which  gives  a  variation  of  only  10  per 
cent  in  the  rates  with  the  minimum  loss  of  head  of  .169  foot  in 
the  entire  filter  assumed  by  him.  The  underdrains  of  the  Berlin 
filters,  according  to  my  calculations,  have  .020  to  .030  foot  friction, 
of  which  an  unusually  large  proportion  is  in  the  gravel,  owing  to 
the  excessive  distances,  in  some  cases  over  80  feet,  which  the 
gravel  is  required  to  carry  the  water.  In  this  case,  using  less  or 
finer  gravel  would  obviously  have  been  fatal,  but  the  friction  as 
well  as  the  expense  of  construction  would  be  much  reduced  by 
using  more  drains  and  less  gravel. 

The  underdrains  might  appropriately  be  made  slightly 
smaller,  with  a  deep  layer  of  fine  sand,  than  under  opposite  con- 
ditions, as  in  this  case  the  increased  friction  in  the  drains 
would  be  no  greater  in  proportion  to  the  increased  friction  in 
the  sand  itself. 

The  underdrains  of  a  majority  of  European  filters  have  water- 
tight pipes  connecting  with  them  at  intervals,  and  going  up 
through  the  sand  and  above  the  water,  where  they  are  open  to 
the  air.  These  pipes  were  intended  to  ventilate  the  underdrains 
and  allow  the  escape  of  air  when  the  filter  is  filled  with  water 
introduced  from  below.  It  may  be  said,  however,  that  in  case 
the  drains  are  surrounded  by  gravel  and  there  is  an  opportunity 
for  the  air  to  pass  from  the  top  of  the  drain  into  the  gravel,  it 
will  so  escape  without  special  provision  being  made  for  it,  and 
go  up  through  the  sand  with  the  much  larger  quantity  of  air 
in  the  upper  part  of  the  gravel  which  is  incapable  of  being  re- 
moved by  pipes  connecting  with  the  drains. 

These  ventilator  pipes  where  they  are  used  are  a  source  of 
much  trouble,  as  unfiltered  water  is  apt  to  run  down  through 
cracks  in  the  sand  beside  them,  and,  under  bad  management, 
unfiltered  water  may  even  go  down  through  the  pipes  them- 
selves. I  am  unable  to  find  that  they  are  necessary,  except  with 
underdrains  so  constructed  that  there  is  no  other  chance  for  the 
escape  of  air  from  the  tops  of  them,  or  that  they  serve  any  useful 


FILTERING   MATERIALS.  45 

purpose,  while  there  are  positive  objections  to  their  use.  In 
some  of  the  newer  filters  they  have  been  omitted  with  satis- 
factory results. 


DEPTH   OF  WATER  ON    THE   FILTERS. 

In  the  older  works  with  but  crude  appliances  for  regulating 
the  rate  of  filtration  and  admission  of  raw  water,  a  considerable 
depth  of  water  was  necessary  upon  the  filter  to  balance  irregu- 
larities in  the  rates  of  filtration  ;  the  filter  was  made  to  be,  to 
a  certain  extent,  its  own  storage  reservoir.  When,  however, 
appliances  of  the  character  to  be  described  in  Chapter  IV  are 
used  for  the  regulation  of  the  incoming  water,  and  with  a  steady 
rate  of  filtration,  this  provision  becomes  quite  superfluous. 

With  open  filters  a  depth  of  water  in  excess  of  the  thickness 
of  any  ice  likely  to  be  formed  is  required  to  prevent  disturb- 
ance or  freezing  of  the  sand  in  winter.  It  is  also  frequently 
urged  that  with  a  deep  water  layer  on  the  filter  the  water  does 
not  become  so  much  heated  in  summer,  but  this  point  is  not  be- 
lieved to  be  well  taken,  for  in  any  given  case  the  total  amount  of 
heat  coming  from  the  sun  to  a  given  area  is  constant,  and  the 
quantity  of  water  heated  in  the  whole  day — that  is,  the  amount 
filtered — is  constant,  and  variations  in  the  quantity  exposed  at 
one  time  will  not  affect  the  average  resulting  increase  in  tempera- 
ture. If  the  same  water  remained  upon  the  filter  without  change 
it  would  of  course  be  true  that  a  thin  layer  would  be  heated 
more  than  a  deep  one,  but  this  is  not  the  case. 

It  is  also  sometimes  recommended  that  the  depth  of  water 
should  be  sufficient  to  form  a  sediment  layer  before  filtration 
starts,  but  this  point  would  seem  to  be  of  doubtful  value,  espe- 
cially where  the  filter  is  not  allowed  to  stand  a  considerable  time 
with  the  raw  water  upon  it  before  starting  filtration. 

It  is  also  customary  to  have  a  depth  of  water  on  the  filter  in 
excess  of  the  maximum  loss  of  head,  so  that  there  can  never  be  a 


46  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

suction  in  the  sand  just  below  the  sediment  layer.  It  may  be 
said  in  regard  to  this,  however,  that  a  suction  below  is  just  as 
effective  in  making  the  water  pass  the  sand  as  an  equal  head 
above.  At  the  Lawrence  Experiment  Station  filters  have  been 
repeatedly  used  with  a  water  depth  of  only  from  6  to  12  inches, 
with  losses  of  head  reaching  6  feet,  without  the  slightest  in- 
convenience. The  suction  only  commences  to  exist  as  the 
increasing  head  becomes  greater  than  the  depth  of  water,  and 
there  is  no  way  in  which  air  from  outside  can  get  in  to  relieve  it, 
In  these  experimental  niters  in  winter,  when  the  water  is  com- 
pletely saturated  with  air,  a  small  part  of  the  air  comes  out  of  the 
water  just  as  it  passes  the  sediment  layer  and  gets  into  reduced 
pressure,  and  this  air  prevents  the  satisfactory  operation  of  the 
filters.  But  this  is  believed  to  be  due  more  to  the  warming  and 
consequent  supersaturation  of  the  water  in  the  comparatively 
warm  places  in  which  the  filters  stand  than  to  the  lack  of  press- 
ure, and  as  not  the  slightest  trouble  is  experienced  at  other 
seasons  of  the  year,  it  may  be  questioned  Avhether  there  would 
be  any  disadvantage  at  any  time  in  a  corresponding  arrangement 
on  a  large  scale  where  warming  could  not  occur. 

The  depths  of  water  actually  used  in  European  filters  with 
the  full  depth  of  sand  are  usually  from  36  to  52  inches.  In  only  a 
very  few  unimportant  cases  is  less  than  the  above  used,  and  only 
a  few  of  the  older  works  use  a  greater  depth,  which  is  not  fol- 
lowed in  any  of  the  modern  plants.  As  the  sand  becomes  re- 
duced in  thickness  by  scraping,  the  depth  of  water  is  correspond- 
ingly increased  above  the  figures  given  until  the  sand  is  replaced. 
The  depth  of  water  on  the  German  covered  filters  is  quite  as 
great  as  upon  corresponding  open  filters.  Thus  the  Berlin  cov- 
ered filters  have  51,  while  the  new  open  filters  at  Hamburg  have 
only  43  inches. 


RATE   OF  FILTRATION  AND   LOSS   OF  HEAD.  47 


CHAPTER  IV. 
RATE  OF  FILTRATION  AND  LOSS  OF  HEAD. 

THE  rate  of  filtration  recommended  and  used  has  been  grad- 
ually reduced  during  the  past  thirty  years.  In  1866  Kirkwood 
found  that  12  vertical  feet  per  day,  or  3.90  million  gallons  per 
acre  daily,  was  recommended  by  the  best  engineers,  and  was 
commonly  followed  as  an  average  rate.  In  1868  the  London 
filters  averaged  a  yield  of  2.18  million  gallons  *  per  acre  daily, 
including  areas  temporarily  out  of  use,  while  in  1885  the  quantity 
had  been  reduced  to  1.61.  Since  that  time  the  rate  has  appar- 
ently been  slightly  increased. 

The  Berlin  filters  at  Stralau  constructed  in  1874  were  built  to 
filter  at  a  rate  of  3.21  million  gallons  per  acre  daily.  The  first 
filters  at  Tegel  were  built  for  a  corresponding  rate,  but  have  been 
used  only  at  a  rate  of  2.57,  while  the  more  recent  filters  were  calcu- 
lated for  this  rate.  The  new  Hamburg  filters,  1892-3,  were  only 
intended  to  filter  at  a  rate  of  1.60  million  gallons  per  acre  daily. 
These  in  each  case  (except  the  London  figures)  are  the  standard 
rates  for  the  filter-beds  actually  in  service. 

In  practice  the  area  of  filters  is  larger  than  is  calculated  from 
these  figures,  as  filters  must  be  built  to  meet  maximum  instead  of 
average  daily  consumptions,  and  a  portion  of  the  filtering  area  usu- 
ally estimated  at  from  5  to  15  per  cent,  but  in  extreme  cases  reach- 
ing 50  per  cent,  is  usually  being  cleaned,  and  so  is  for  the  time  out 
of  service.  In  some  works  also  the  rate  of  filtration  on  starting  a 
filter  is  kept  lower  than  the  standard  rate  for  a  day  or  two,  or  the 
first  portion  of  the  effluent,  supposed  to  be  of  inferior  quality,  is 

*  The  American  gallon  is  used  throughout  this  book;  the  English  gallon  is  one  fifth 
larger. 


48  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

wasted,  the  amount  so  lost  reaching  in  an  extreme  case  9  to  14  per 
cent  of  the  total  quantity  of  water  filtered.*  In  many  of  the  older 
works  also,  there  is  not  storage  capacity  enough  for  filtered  water 
to  balance  the  hourly  fluctuations  in  consumption,  and  the  filters 
must  be  large  enough  to  meet  the  maximum  hourly  as  well  as 
the  maximum  daily  requirements.  For  these  reasons  the  actual 
quantity  of  water  filtered  in  a  year  is  only  from  50  to  75  per  cent 
of  what  would  be  the  case  if  the  entire  area  of  the  filters  worked 
constantly  at  the  full  rate.  A  statement  of  the  actual  yields  of  a 
number  of  filter  plants  is  given  in  Appendix  IV.  The  figures  for 
the  average  annual  yields  can  be  taken  as  quite  reliable.  The 
figures  given  for  rate,  in  many  cases,  have  little  value,  owing  to 
the  different  ways  in  which  they  are  calculated  at  different  places. 
In  addition  most  of  the  old  works  have  no  adequate  means  of 
determining  what  the  rate  at  any  particular  time  and  for  a  single 
filter  really  is,  and  statements  of  average  rates  have  only  limited 
value.  The  filters  at  Hamburg  are  not  allowed  to  filter  faster 
than  i. 60  or  those  at  Berlin  faster  than  2.57  million  gallons  per 
acre  daily,  and  adequate  means  are  provided  to  secure  this  con- 
dition. Other  German  works  aim  to  keep  within  the  latter  limit. 
Beyond  this,  unless  detailed  information  in  regard  to  methods  is 
presented,  statements  of  rate  must  be  taken  with  some  allowance. 

EFFECT   OF   RATE   UPON   COST   OF   FILTRATION. 

The  size  of  the  filters  required,  and  consequently  the  first  cost, 
depends  upon  the  rate  of  filtration,  but  with  increasing  rates  the 
cost  is  not  reduced  in  the  same  proportion  as  the  increase  in 
rate,  since  the  allowance  for  area  out  of  use  is  sensibly  the  same 
for  high  and  low  rates,  and  in  addition  the  operating  expenses 
depend  upon  the  quantity  filtered  and  not  upon  the  filtering 
area.  Thus,  to  supply  10  million  gallons  at  a  maximum  rate  of  2 
million  gallons  per  acre  daily  we  should  require  10  ~  2  =  5  acres 
-|-  i  acre  reserve  for  cleaning  =  6  acres,  while  with  a  rate  twice 

*  Piefke,  Zeitschrift  Jiir  Hygiene,  1894,   p.  177. 


RATE   OF  FILTRATION  AND   LOSS   OF  HEAD.  49 

as  great,  and  with  the  same  reserve  (since  the  same  amount  of 
cleaning  must  be  done,  as  will  be  shown  below),  we  should  re- 
quire 10  -7-  4  +  i  =  3.5  acres,  or  58  per  cent  of  the  area  required 
for  the  lower  rate.  Thus  beyond  a  certain  point  increasing  the 
rate  does  not  effect  a  corresponding  reduction  in  the  first  cost. 

The  operating  cost  for  the  same  quantity  of  water  filtered 
does  not  appear  to  be  appreciably  affected  by  the  rate.  It  is 
obvious  that  at  high  rates  filters  will  became  clogged  more 
rapidly,  and  will  so  require  to  be  scraped  oftener  than  at  low 
rates,  and  it  might  naturally  be  supposed  that  the  clogging 
would  increase  more  rapidly  than  the  rates,  but  this  does  not 
seem  to  be  the  case.  At  the  Lawrence  Experiment  Station, 
under  strictly  parallel  conditions  and  with  identically  the  same 
water,  filters  running  at  various  rates  became  clogged  with  a 
rapidity  directly  proportional  to  the  rates,  so  that  the  quantities 
of  water  filtered  between  scrapings  under  any  given  conditions 
are  the  same  whether  the  rate  is  high  or  low. 

The  statistics  bearing  upon  this  point  are  interesting,  if  not 
entirely  conclusive.  There  were  eleven  places  in  Germany  filtering 
river  waters,  from  which  statistics  were  available  for  the  year 
1891-92.  Of  these  there  were  four  places  with  high  rates, 
Liibeck,  Stettin,  Stuttgart,  and  Magdeburg,  yielding  3.70  million 
gallons  per  acre  daily,  which  filtered  on  an  average  59  million  gallons 
per  acre  between  scrapings.  Three  other  places,  Breslau,  Altona, 
and  Frankfurt,  yielding  1.85,  passed  on  an  average  55  million 
gallons  per  acre  between  scrapings,  and  four  other  places, 
Bremen,  Konigsberg,  Brunswick  and  Posen,  yielding  1.34  million 
gallons  per  acre  daily,  passed  only  40  million  gallons  per  acre 
between  scrapings.  The  works  filtering  at  the  highest  rates  thus 
filtered  more  water  in  proportion  to  the  sand  clogged  than  did 
those  filtering  more  slowly,  but  I  cannot  think  that  this  was  the 
result  of  the  rate.  It  is  more  likely  that  some  of  the  places  have 
clearer  waters  than  others,  and  that  this  both  allows  the  higher 
rate  and  causes  less  clogging  than  the  more  turbid  waters. 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


EFFECT   OF   RATE    UPON   EFFICIENCY   OF   FILTRATION. 

The  effect  of  the  rate  of  filtration  upon  the  quality  of  the 
effluent  has  been  repeatedly  investigated.  The  efficiency  almost 
uniformly  decreases  rapidly  with  increasing  rate.  Frankel  and 
Piefke*  first  found  that  with  the  high  rates  the  number  of  bac- 
teria passing  some  experimental  filters  was  greatly  increased. 
Piefkef  afterward  repeated  these  experiments,  eliminating  some 
of  the  features  of  the  first  series  to  which  objection  was  made, 
and  confirmed  the  first  results.  The  results  were  so  marked 
that  Piefke  was  led  to  recommend  the  extremely  low  limit  of 
1.28  million  gallons  per  acre  daily  as  the  safe  maximum  rate  of 
filtration,  but  he  has  since  repeatedly  used  2.57  million  gallons. 

Kiimmel,J  on  the  other  hand,  in  a  somewhat  limited  series 
of  experiments,  was  unable  to  find  any  marked  connection 
between  the  rate  and  the  efficiency,  a  rate  of  2.57  giving  slightly 
better  results  than  rates  of  either  1.28  or  5.14. 

The  admirably  executed  experiments  made  at  Zurich  in 
1886-8  upon  this  point,  which  gave  throughout  negative  results, 
have  but  little  value  in  this  connection,  owing  to  the  extremely 
low  number  of  bacteria  in  the  original  water. 

At  Lawrence  in  1892  the  following  percentages  of  bacteria 
(B.  prodigiosus]  passed  at  the  respective  rates : 


No.  of 
Filter. 

Depth. 

Effective 
Size  of 
Sand. 

Rate.     Million  gallons  per  acre  daily. 

0.5 

1  .0 

!-5 

2.O 

3-o 

33A 

34A 
36A 

% 

39 

40 
42 

60 
60 
60 
60 
24 
12 
12 
12 

0.14 
0.09 
O.2O 
0.20 
0.20 
O.2O 
0.20 
0.20 

O.OO2 
O.OOI 

0.040 

0.005 

O.O2O 

0.050 
0.010 

0.140 

0.136 
O.IIO 
0.080 
0.090 

o.  150 

0.050 

O.OlS 
0.014 

0.016 

0.070 
0.070 

O.3IO 
0.520 

0.550 



Ave 

racre.   . 

0.010 

0.048 

0.067 

0.088 

0.356 

*  Zeitschrift  fur  Hygiene \  1891,  page  38. 
\JournalfurGas-  u.    Wasserversorgung,  1891,  208  and  22i 
\  Journal  fur  Gas-  u.  Wasserversorgung,  1893,  161. 


RATE   OF  FILTRATION  AND   LOSS   OF  HEAD.  5  I 

These  results  show  a  very  marked  decrease  in  efficiency  with 
increasing  rates,  the  number  of  bacteria  passing  increasing  in 
general  as  rapidly  as  the  square  of  the  rate.  The  1893  results 
also  showed  decreased  efficiency  with  high  rates,  but  the  range 
in  the  rates  under  comparable  conditions  was  less  than  in  1892, 
and  the  bacterial  differences  were  less  sharply  marked. 

While  the  average  results  at  Lawrence,  as  well  as  most  of  the 
European  experiments,  show  greatly  decreased  efficiency  with 
high  rates,  there  are  many  single  cases,  particularly  with  deep 
layers  of  not  too  coarse  sand,  where,  as  in  Kiimmel's  experiments, 
there  seems  to  be  little  connection  between  the  rate  and  effi- 
ciency. An  explanation  of  these  apparently  abnormal  results 
will  be  given  in  Chapter  VI. 

It  is  commonly  stated  *  that  every  water  has  its  own  special 
rate  of  filtration,  which  must  be  determined  by  local  experiments, 
and  that  this  rate  may  vary  widely  in  different  cases.  Thus  it  is 
possible  that  the  rate  of  1.60  adopted  at  Hamburg  for  the  tur- 
bid Elbe  water,  the  rate  of  2.57  used  at  Berlin,  and  about  the  same 
at  London  for  much  clearer  river-  waters,  and  the  rate  of  7.50 
used  at  Zurich  for  the  almost  perfectly  clear  lake-water  are  in 
each  case  the  most  suitable  for  the  respective  waters.  In  other 
cases  however,  where  rates  much  above  2.57  are  used  for  river- 
waters,  as  at  Liibeck  and  Stettin,  there  is  a  decided  opinion  that 
these  rates  are  excessive,  and  in  these  instances  steps  are  now 
being  taken  to  so  increase  the  filtering  areas  as  to  bring  the  rates 
within  the  limit  of  2.57  million  gallons  per  acre  daily. 

From  the  trend  of  European  practice  it  would  seem  that  for 
American  river-waters  the  rate  of  filtration  should  not  exceed 
2.57  in  place  of  the  3.90  million  gallons  per  acre  daily  recom- 
mended by  Kirkwood,  or  even  that  a  somewhat  lower  rate  might 
be  desirable  in  some  cases.  Of  course,  in  addition  to  the  area 

*  Samuelson's  translation  of  Kirkwood's  "Filtration  of  River-waters;"  Lindley, 
Die  Nutzbarmachung  des  Flusswassers,  Journal  fiir  Gas-  u.  Wasserversorgung,  1890, 
501;  Kaiserlichen  Gesundheitsamt,  Grundsatze  fiir  die  Reinigung  von  Oberflachemvas- 
ser  durch  Sandfiltration;  Journal  fiir  Gas-  u.  Wasserversorgung,  1894,  Appendix  I. 


• 


52  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

necessary  to  give  this  rate,  a  reserve  for  fluctuating  rates  and  for 
cleaning  should  be  provided,  reducing  the  average  yield  to  2.00, 
1.50,  or  even  less.  In  the  case  of  water  from  clear  lakes,  ponds, 
or  storage  reservoirs,  especially  when  they  are  not  subject  to  ex- 
cessive sewage  pollution  or  to  strong  algae  growths,  it  would 
seem  that  rates  somewhat  and  perhaps  in  some  cases  very  much 
higher  (as  at  Zurich)  could  be  satisfactorily  used. 

THE    LOSS   OF   HEAD. 

The  loss  of  head  is  the  difference  between  the  heads  of  the 
waters  above  and  below  the  sand  layer,  and  represents  the  fric- 
tional  resistance  of  that  layer.  When  a  filter  is  quite  free  from 
clogging  this  frictional  resistance  is  small,  but  gradually  increases 
with  the  deposit  of  a  sediment  layer  from  the  water  filtered  until 
it  becomes  so  great  that  the  clogging  must  be  removed  by 
scraping  before  the  process  can  be  continued.  After  scraping 
the  loss  of  head  is  reduced  to,  or  nearly  to,  its  original 
amount.  With  any  given  amount  of  clogging  the  loss  of  head  is 
directly  proportional  to  the  rate  of  filtration ;  that  is,  if  a  filter 
partially  clogged,  filtering  at  a  rate  of  i.o,  has  a  frictional  resist- 
ance of  0.5  ft,  the  resistance  will  be  doubled  by  increasing  the 
rate  to  2.00  million  gallons  per  acre  daily,  provided  no  disturb- 
ance of  the  sediment  layer  is  allowed.  This  law  for  the  frictional 
resistance  of  water  in  sand  alone  also  applies  to  the  sediment  layer, 
as  I  have  found  by  repeated  tests,  although  in  so  violent  a  change 
as  that  mentioned  above,  the  utmost  care  is  required  to  make  the 
change  gradually  and  prevent  compression  or  breaking  of  the 
.sediment  layer.  From  this  relation  between  the  rate  of  filtration 
and  the  loss  of  head  it  is  seen  that  the  regulation  of  either  in 
volves  the  regulation  of  the  other,  and  it  is  a  matter  of  indiffer- 
ence which  is  directly  and  which  indirectly  controlled. 

REGULATION    OF  THE    RATE  AND   LOSS   OF   HEAD    IN  THE    OLDER 

FILTERS. 

In  the  older  works,  and  in  fact  in  all  but  a  few  of  the  newest 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD. 


53 


works,  the  underdrains  of  the  filters  connect  directly  through  a 
pipe  with  a  single  gate  with  the  pure-water  reservoir  or  pump- 
well,  which  is  so  built  that  the  water  in  it  may  rise  nearly  or 
quite  as  high  as  that  standing  upon  the  filter. 

A  typical  arrangement  of  this  sort  was  used  at  the  Stralau 
works  at  Berlin  (now  discontinued),  Fig.  5.     With  this  arrange- 


FIG.  5. — SIMPLEST  FORM  OF  REGULATION  :   STRALAU  FILTERS  AT  BERLIN. 

ment  the  rate  of  filtration  is  dependent  upon  the  height  of  water 
in  the  reservoir  or  pump-well,  and  so  upon  the  varying  con- 
sumption. When  the  water  in  the  receptacle  falls  with  increas- 
ing consumption  the  head  is  increased,  and  with  it  the  rate  of 
filtration,  while,  on  the  other  hand,  with  decreasing  draft  and 
rising  water  in  the  reservoir,  the  rate  of  filtration  decreases  and 
would  eventually  be  stopped  if  no  water  were  used.  This  very 
simple  arrangement  thus  automatically,  within  limits,  adjusts 
the  rate  of  filtration  to  the  consumption,  and  at  the  same  time 
always  gives  the  highest  possible  level  of  water  in  the  pump- 
well,  thus  also  economizing  the  coal  required  for  pumping. 

In  plants  of  this  type  the  loss  of  head  may  be  measured  by 
floats  on  little  reservoirs  built  for  that  purpose,  connected  with 
the  underdrains ;  but  more  often  there  is  no  means  of  determining 
it,  although  the  maximum  loss  of  head  at  any  time  is  the  difference 
between  the  levels  of  the  water  on  the  filter  and  in  the  reser- 
voir, or  the  outlet  of  the  drain-pipe,  in  case  the  latter  is  above 


54  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

the  water-line  in  the  reservoir.  The  rate  of  nitration  can  only  be 
measured  with  this  arrangement  by  shutting  off  the  incoming 
water  for  a  definite  interval,  and  observing  the  distance  that  the 
water  on  the  filter  sinks.  The  incoming  water  is  regulated  sim- 
ply by  a  gate,  which  a  workman  opens  or  closes  from  time  to 
vtime  to  hold  the  required  height  of  water  on  the  filter. 

The  only  possible  regulation  of  the  rate  and  loss  of  head  is 
effected  by  a  partial  closing  of  the  gate  on  the  outlet-pipe,  by 
which  the  freshly-cleaned  filters  with  nearly-closed  gates  are  kept 
from  filtering  more  rapidly  than  the  clogged  filters,  the  gates  of 
which  are  opened  wide.  Often,  however,  this  is  not  done,  and 
then  the  fresh  filters  filter  many  times  as  rapidly  as  those  which 
are  partially  clogged. 

A  majority  of  the  filters  now  in  use  are  built  more  or  less  upon 
this  plan,  including  most  of  those  in  London  and  also  the  Altona 
works,  which  had  such  a  favorable  record  with  cholera  in  1892. 

The  invention  and  application  of  methods  of  bacterial  exam- 
ination in  the  last  years  have  led  to  different  ideas  of  filtration 
from  those  which  influenced  the  construction  of  the  earlier 
plants.  As  a  result  it  is  now  regarded  as  essential  by  most 
German  engineers  *  that  each  filter  shall  be  provided  with  de- 
vices for  measuring  accurately  and  at  any  time  both  the  rate  of 
filtration  and  the  loss  of  head,  and  for  controlling  them,  and  also 
for  making  the  rate  independent  of  consumption  by  reservoirs 
for  filtered  water  large  enough  to  balance  hourly  variations 
{capacity  J  to  \  maximum  daily  quantity)  and  low  enough  so  that 
they  can  never  limit  the  rate  of  filtration  by  causing  back-water  on 
the  filters.  These  points  are  now  insisted  upon  by  the  German 
Imperial  Board  of  Health,f  and  all  new  filters  are  built  in  accord- 
ance with  them,  while  most  of  the  old  works  are  being  built  over 
to  conform  to  the  requirements. 

*  Lindley,  Journal  fur  Gas- u.    IVasserversorgung,    1890,  501  ;  Grahn,  Journal  fur 
Gas-  tt.   Wasserversorgung,  1890,  511  ;  Halbertsma,  Journal  fur  Gas.  u.   Wua 
gung,  1892,  686;   Piefke,  Zeitschrift  fur  Hygiene,  1894,  151  ;  and  others. 

f  Appendix  I. 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD. 


55 


APPARATUS   FOR   REGULATING   THE   RATE  AND    LOSS   OF   HEAD. 

Many  appliances  have  been  invented  for  the  regulation  of  the 
rate  and  loss  of  head.  In  the  apparatus  designed  by  Gill  and  used 
at  both  Tegel  and  Miiggel  at  Berlin  the  regulation  is  effected  by 
partially  closing  a  gate  through  which  the  effluent  passes  into  a 
chamber  in  which  the  water-level  is  practically  constant  (Fig.  6). 


1 L 


T 


10  15  20  25  Feet 

FIG.  6. — REGULATION  APPARATUS  AT  BERLIN  (TEGEL). 

The  rate  is  measured  by  the  height  of  water  on  the  weir  which 
serves  as  the  outlet  for  this  second  chamber  into  a  third  connect- 
ing with  the  main  reservoir,  while  the  loss  of  head  is  shown  by 
the  difference  in  height  of  floats  upon  water  in  the  first  chamber, 
representing  the  presure  in  the  underdrains,  and  upon  water  in 
connection  with  the  raw  water  on  the  filter.  From  the  respective 
heights  of  the  three  floats  the  attendant  can  at  any  time  see  the 
rate  of  filtration  and  the  loss  of  head,  and  when  a  change  is  re- 
quired it  is  effected  by  moving  the  gate. 

In  the  apparatus  designed  in  1866  by  Kirkwood  for  St.  Louis 
and  never  built  (Fig.  7)  the  loss  of  head  was  directly,  and  the  rate 
indirectly,  regulated  by  a  movable  weir,  which  was  to  have  been 
lowered  from  time  to  time  by  the  attendant  to  secure  the  re- 
quired results.  This  plan  is  especially  remarkable  as  it  meets 


50  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

the  modern  requirements  of  a  regular  rate  independent  of 
rate  of  consumption  and  of  the  water-level  in  the  reservoir,  and 
also  allows  continual  measurements  of  both  rate  (height  of  water 


AM. BANK  NOTE  CO.H.Y, 


f 


8  Meters 


I'TT'i'        »        <       .' 

0  i  '  ITJ  '  '  15  '  '  2!0       '        '25  Feet 

FIG.  7. — REGULATION  APPARATUS  AND  SECTION  OF  FILTER  RECOMMENDED  FOR 
ST.  Louis  BY  KIRKWOOD  IN  1866. 

on  the  weir)  and  head  (difference  in  water-levels  on  filter  and  in 
effluent  chamber)  to  be  made,  and  control  of  the  same  by  the 
position  of  the  weir.  *Mr.  KirkwooS  found  no  filters  in 'Europe 
with  such  appliances,  and  it  was  many  years  after  his  report 
was  published  before  similar  devices  were  used,  but  they  are 
now  regarded  as  essential. 

The  regulators  for  new  filters  at  Hamburg  (Fig.  8)  are  built 


FIG.  8. — REGULATION  APPARATUS  USED  AT  HAMBURG. 

upon  the  principle  of  Kirkwood's  device,  but  provision  is  made 
for  a  second  measurement  of  the  water  if  desired  by  the  loss  of 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD. 


57 


head  in  passing  a  submerged  orifice.  Both  the  rate  and  loss  of 
head  are  indicated  by  a  float  on  the  first  chamber  connecting 
directly  with  the  underdrain,  which  at  the  same  time  indicates 
the  head  on  a  fixed  scale,  the  zero  of  which  corresponds  to  the 
height  of  the  water  above  the  filter,  and  the  rate  upon  a  scale 
moving  with  the  weir,  the  zero  of  which  corresponds  with 
the  edge  of  the  weir.  The  water  on  the  filter  is  held  at  a  per- 
fectly constant  level. 

The  regulators  in  use  at  Worms  and  those  recently  introduced 
at  Magdeburg  act  upon  the  same  principle,  but  the  levels  of 
the  water  on  the  filters  are  allowed  to  fluctuate,  and  the  weirs 
and  in  fact,  the  whole  regulating  appliances  are  mounted  on 
big  floats  in  surrounding  chambers  of  water  connecting  with  the 
unfiltered  water  on  the  filters.  I  am  unable  to  find  any 
advantages  in  these  appliances,  and  they  are  much  more 
complicated  than  the  forms  shown  by  the  cuts. 


APPARATUS   FOR  REGULATING  THE   RATE   DIRECTLY. 

The  above-mentioned  regulators  control  directly  the  loss  of 
head,  and  only  indirectly  the  rate  of  filtration.     The  regulators 


0   '  I   '  '  fo  '  "  JT    "    '      •  Feet 

FIG.  g.— LINDLEY'S  REGULATION  APPARATUS  AT  WARSAW,  RUSSIA. 

at  Warsaw  were  designed  by  Lindley  to  regulate  the  rate  di- 
rectly and  make  it  independent  of  the  loss  of  head.  The  quan- 
tity of  water  flowing  away  is  regulated  by  a  float  upon  the  water 


58  FILTRATION   OF  PUBLIC  WATER-SUPPLIES. 

in  the  effluent  chamber,  which  holds  the  top  of  the  telescope  out- 
let-pipe a  constant  distance  below  the  surface  and  so  secures  a 
constant  rate.  As  the  friction  of  the  filter  increases  the  float 
sinks  with  the  water  until  it  reaches  bottom,  when  the  filter  must 
be  scraped.  A  counter-weight  reduces  the  weight  on  the  float, 
and  at  the  same  time  allows  a  change  in  the  rate  when  desired. 
This  apparatus  is  automatic.  All  of  the  other  forms  described 
require  to  be  occasionally  adjusted  by  the  attendant,  but  the  at- 
tention they  require  is  very  slight,  and  watchmen  are  always  on 
duty  at  large  plants,  who  can  easily  watch  the  regulators.  The 
Warsaw  apparatus  is  reported  to  work  very  satisfactorily,  no 
trouble  being  experienced  either  by  leaking  or  sticking  of  the 
telescope-joint,  which  is  obviously  the  weakest  point  of  the 
device,  but  fortunately  a  perfectly  tight  joint  is  not  essential  to 
the  success  of  the  apparatus.  Regulators  acting  upon  the  same 
principle  have  recently  been  installed  at  Zurich,  where  they  are 
operating  successfully. 

Burton*  has  described  an  ingenious  device  designed  by  him 
for  the  filters  at  Tokyo,  Japan.  It  consists  of  a  double  acting 
valve  of  gun  metal  (similar  to  that  shown  by  Fig.  u),  through 
which  the  effluent  must  pass.  This  valve  is  opened  and  closed 
by  a  rod  connecting  with  a  piston  in  a  cylinder,  the  opposite 
sides  of  which  connect  with  the  effluent  pipe  above  and  below 
a  point  where  the  latter  is  partially  closed,  so  that  the  valve  is 
opened  and  closed  according  as  the  loss  of  head  in  passing  this 
obstruction  is  below  or  above  the  amount  corresponding  to  the 
desired  rate  of  filtration. 

The  use  of  the  Venturi  meter  in  connection  with  the  regula- 
tion of  filters  would  make  an  interesting  study,  and  has,  I  be- 
lieve, never  been  considered. 

*  The  Water  Supply  of  Towns.     London,  1894. 


REGULATOR-HOUSE,  SHOWING  RATE  OF  FILTRATION  AND 
Loss  OF  HEAD  ON  THE  OUTSIDE,   BREMEN. 


INLET  FOR  ADMISSION  OF  RAW  WATER  TO  A  FILTER, 
EAST  LONDON. 

[To  face fage  58.] 


OF   THE 

UNIVERSITY 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD. 


59 


APPARATUS   FOR   REGULATING  THE    HEIGHT  OF  WATER   UPON 

FILTERS. 

It  will  be  seen  by  reference  to  the  diagrams  of  the  Berlin  and 
Hamburg  effluent  regulators  (Figs.  6  and  8)  that  their  perfect 
operation  is  dependent  upon  the  maintenance  of  a  constant  water- 
level  upon  the  filters.  The  old-fashioned  adjustment  of  the  inlet- 
gate  by  the  attendant  is  hardly  accurate  enough. 

The  first  apparatus  for  accurately  and  automatically  regulat- 
ing the  level  of  the  water  upon  the  filters  was  constructed  at 
Leeuwarden,  Holland,  by  the  engineer,  Mr.  Halbertsma,  who  has 
since  used  a  similar  device  at  other  places,  and  improved  forms 
of  which  are  now  used  at  Berlin  and  at  Hamburg. 

At  Berlin  (Muggel)  the  water-level  is  regulated  by  a  float 
upon  the  water  in  the  filter  which  opens  or  shuts  a  balanced 
double  valve  on  the  inlet-pipe  directly  beneath,  as  shown  in  Fig. 
10.  It  is  not  at  all  necessary  that  this  valve  should  shut  water- 
tight ;  it  is  only  necessary  that  it  should  prevent  the  continuous 
inflow  from  becoming  so  great  as  to  raise  the  water-level,  and 


FIG.  10. — REGULATION  OF  INFLOW  USED  AT  MUGGEL,  BERLIN. 

for  this  reason  loose,  easily-working  joints  are  employed.  The 
apparatus  is  placed  in  a  little  pit  next  to  the  side  of  the  filter, 
and  the  overflowing  water  is  prevented  from  washing  the  sand 
by  paving  the  sand  around  it  for  a  few  feet. 

At  Hamburg  the  same  result  is  obtained  by  putting  the  valve 


6o 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


in  a  special  chamber  outside  of  the  filter  and  connected  with  the 
float  by  a  walking-beam  (Fig.  11). 

The  various  regulators  require  to  be  protected  from  cold  and 
ice  by  special  houses,  except  in  the  case  of  covered  filters,  where 
they  can  usually  be  arranged  with  advantage  in  the  filter  itself. 


0  1  2  3  4  5  61 

1  i     I"  r    i~|     i*l    F     ii     i     •     I    *     I     ii     i     "I 

0  6  10  15  20 


6  Meters 
20  Feet 

FIG.  u. — REGULATION  OF  INFLOW  USED  AT  HAMBURG. 


In  regard  to  the  choice  of  the  form  of  regulator  for  both  the 
inlets  and  outlets  of  filters,  so  far  as  I  have  been  able  to  ascer- 
tain, each  of  the  modern  forms  described  as  in  use  performs  its 
functions  satisfactorily,  and  in  special  cases  any  of  them  could 
properly  be  selected  which  would  in  the  local  conditions  be  the 
simplest  in  construction  and  operation. 


LIMIT  TO   THE    LOSS   OF   HEAD. 

The  extent  to  which  the  loss  of  head  is  allowed  to  go  before 
filters  are  cleaned  differs  widely  in  the  different  works,  some  of 
the  newer  works  limiting  it  sharply  because  it  is  believed  that 
low  bacterial  efficiency  results  when  the  pressure  is  too  great, 
although  the  frequency  of  cleaning  and  consequently  the  cost  of 
operation  are  thereby  increased. 

At  Darlington,  England,  I  believe  as  a  result  of  the  German 
theories,  the  loss  of  head  is  limited  to  about  18  inches  by  a 
masonry  weir  built  within  the  last  few  years.  At  Berlin,  both  at 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD,  6 1 

Tegel  and  Miiggel,  the  limit  is  24  inches,  while  at  the  new  Ham- 
burg works  28  inches  are  allowed.  At  Stralau  in  1893  an  effort 
was  made  to  not  exceed  a  limit  of  40  inches,  but  previously  heads 
up  to  60  inches  were  used,  which  corresponds  with  the  56  inches 
used  at  Altona ;  and,  in  the  other  old  works,  while  exact  iniorma- 
tion  is  not  easily  obtained  because  of  imperfect  records,  I  am  con- 
vinced that  heads  of  60  or  even  80  inches  are  not  uncommon. 
At  the  Lawrence  Experiment  Station  heads  of  70  inches  have 
generally  been  used,  although  some  filters  have  been  limited  to 
36  and  24  inches. 

In  1866  Kirkwood  became  convinced  that  the  loss  of  head 
should  not  go  much  above  30  inches,  first,  because  high  heads 
would,  by  bringing  extra  weight  upon  the  sand,  make  it  too 
compact,  and,  second,  because  when  the  pressure  became  too 
great  the  sediment  layer  on  the  surface  of  the  sand,  in  which 
most  of  the  loss  of  head  occurs,  would  no  longer  be  able  to 
support  the  weight  and,  becoming  broken,  would  allow  the 
water  to  pour  through  the  comparatively  large  resulting  open- 
ings at  greatly  increased  rates  and  with  reduced  efficiency. 

In  regard  to  the  first  point,  a  straight,  even  pressure  many 
times  that  of  the  water  on  the  filter  is  incapable  of  compressing 
the  sand.  It  is  much  more  the  effect  of  the  boots  of  the  work- 
men when  scraping  that  makes  the  sand  compact.  I  have  found 
sand  in  natural  banks  at  Lawrence  70  or  80  feet  below  the  sur- 
face, where  it  had  been  subjected  to  corresponding  pressure  for 
thousands  of  years,  to  be  quite  as  porous  as  when  packed  in 
water  in  experimental  filters  in  the  usual  way. 

The  second  reason  mentioned,  or,  as  I  may  call  it,  the  break- 
ing-through theory,  is  very  generally  if  not  universally  accepted 
by  German  engineers,  and  this  is  the  reason  for  the  low  limit 
commonly  adopted  by  them. 

A  careful  study  of  the  results  at  Lawrence  fails  to  show  the 
slightest  deterioration  of  the  effluents  up  to  the  limit  used,  72 
inches.  Thus  in  1892,  taking  only  the  results  of  the  continuous 


62  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

filters  of  full  height  (Nos.  33A,  34A,  36A,  and  37),  we  find  that 
for  the  three  days  before  scraping,  when  the  head  was  nearly  72 
inches,  the  averge  number  of  bacteria  in  the  effluents  was  31  per 
cc.,  while  for  the  three  days  after  scraping,  with  very  low  heads, 
the  number  was  47.  The  corresponding  numbers  of  B.  prodigio- 
sus* were  i.i  and  2.7.  This  shows  better  work  with  the  highest 
heads,  but  is  open  to  the  objection  that  the  period  just  after  scrap- 
ing, owing  to  the  disturbance  of  the  surface,  is  commonly  sup- 
posed to  be  a  period  of  low  efficiency. 

To  avoid  this  criticism  in  calculating  the  corresponding 
results  for  1893,  the  numbers  of  the  bacteria  for  the  intermediate 
days  which  could  not  have  been  influenced  either  by  scraping 
or  by  excessive  head  are  put  side  by  side  with  the  others.  Tak- 
ing these  results  as  before  for  continuous  filters  72  inches  high,, 
and  excluding  those  with  extremely  fine  sands  and  a  filter  which 
was  only  in  operation  a  short  time  toward  the  end  of  the  year, 
we  obtain  the  following  results: 

Water  B. 

Bacteria  Prodigiosus 

per  cc.  per  cc. 

Average  ist  day  after  scraping,  low  heads 79  6.1 

2d    "        "  "        "     44  4.1 

"      3d    "        "  "  "        "     -.45  3-6 

Intermediate  days,  medium  heads 59  4.5 

Second  from  last  day,  heads  of  nearly  72  inches 66  2.7 

Next  to  the  last  day,       "        "      "        "        "       56  3.2 

Last  day,  "        "       "        "         "       83  2.5 

These  figures  show  a  very  slight  increase  of  the  water  bac- 
teria in  the  effluent  as  the  head  approaches  the  limit,  but  no 
such  increase  as  might  be  expected  from  a  breaking  through  of 
the  sediment  layer,  and  the  B.  prodigiosus  which  is  believed  to 
better  indicate  the  removal  of  the  bacteria  of  the  original  water, 

*  A  special  species  of  bacteria  artificially  added  to  secure  more  precise  information 
in  regard  to  the  passage  of  germs  through  the  filter. 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD.  63 

actually  shows  a  decrease,  the  last  day  being  the  best  day  of  the 
whole  period. 

The  Lawrence  results,  then,  uniformly  and  clearly  point  to  a 
conclusion  directly  opposite  to  the  commonly  accepted  view, 
and  I  have  thus  been  led  to  examine  somewhat  closely  the 
grounds  upon  which  the  breaking-through  theory  rests. 

The  two  works  which  have  perhaps  contributed  most  to  the 
theories  of  filtration  are  the  Stralau  and  Altona  works.  After 
examining  the  available  records  of  these  works,  I  am  quite  con- 
vinced that  at  these  places  there  has  been,  at  times  at  least,  de- 
creased efficiency  with  high  heads.  For  the  Stralau  works 
this  is  well  shown  by  Piefke's  plates  in  the  Zeitschrift  fiir  Hygiene, 
1894,  after  page  188.  In  both  of  these  works,  however,  the  ap- 
paratus (or  lack  of  apparatus)  for  regulating  the  rate  is  that  shown 
by  Fig.  5,  page  49,  and  the  rate  of  filtration  is  thus  dependent 
upon  the  rate  of  consumption  and  the  height  of  water  in  the 
reservoir.  At  the  Stralau  works,  at  the  time  covered  by  the 
above-mentioned  diagrams,  the  daily  quantity  of  water  filtered 
was  27  times  the  capacity  of  the  reservoir,  and  the  rate  of  filtra- 
tion must  consequently  have  adapted  itself  to  the  hourly  con- 
sumptions. The  data  which  formed  the  basis  of  Kirkwood's 
conclusions  are  not  given  in  detail,  but  it  is  quite  safe  to  assume 
that  they  were  obtained  from  filters  regulated  as  those  at  Altona 
and  Stralau  are  regulated,  and  what  is  said  in  regard  to  the 
latter  will  apply  equally  to  his  results. 

Piefke*  shows  that  among  the  separate  filters  at  Stralau,  all 
connected  with  the  same  pure-water  reservoir,  those  connected 
through  the  shorter  pipes  gave  poorer  effluents  than  the  more 
remote  filters,  and  he  attributes  the  difference  to  the  frictional 
resistance  of  the  connecting  pipes,  which  helped  to  prevent  ex- 
cessive rates  in  the  filters  farthest  away  when  the  water  in  the 
reservoir  became  low,  and  thus  the  fluctuations  in  the  rates  in 
these  filters  were  less  than  in  those  close  to  the  reservoir.  He 


*  Zfitschrift  fiir  Hygiene,  1894,  p.  173. 


64  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

does  not,  however,  notice,  in  speaking  of  the  filters  in  which 
the  decreased  efficiencies  with  high  heads  were  specially  marked, 
that  they  follow  in  nearly  the  same  order,  and  that  of  the  four 
open  filters  mentioned  three. were  near  the  reservoir  and  only 
one  was  separated  by  a  comparatively  long  pipe,  indicating  that 
the  deterioration  with  high  heads  was  only  noticeable,  or  at 
least  was  much  more  conspicuous,  in  those  filters  where  the  rates 
fluctuated  most  violently. 

It  requires  no  elaborate  calculation  to  show  that  of  two  filters 
connected  with  the  same  pure-water  reservoir,  as  shown  by  Fig. 
5,  with  only  simple  gates  on  the  connecting  pipes,  one  of  them 
clean  and  throttled  by  a  nearly  closed  gate,  so  that  the  normal 
pressure  behind  the  gate  is  above  the  highest  level  of  water 
in  the  reservoir,  and  the  other  clogged  so  that  the  normal 
pressure  of  the  water  in  the  drain  is  considerably  below  the 
highest  level  of  the  water  in  the  reservoir,  the  latter  will  suffer 
much  the  more  severe  shocks  with  fluctuating  water-levels ;  and 
the  fact  being  admitted  that  fluctuating  levels  are  unfavorable, 
we  must  go  farther  and  conclude  that  the  detrimental  action 
will  increase  with  increasing  loss  of  head.  I  am  inclined  to 
think  that  this  theory  is  adequate  to  explain  the  Stralau  and 
Altona  results  without  resource  to  the  breaking-through  theory. 

While  the  above  does  not  at  all  prove  the  breaking-through 
theory  to  be  false,  it  explains  the  results  upon  which  it  rests  in 
another  way,  and  can  hardly  fail  to  throw  so  much  doubt  upon 
it  as  to  make  us  refuse  to  allow  its  application  to  those  works 
where  a  regular  rate  of  filtration  is  maintained  regardless  of 
variations  in  the  consumption,  until  proof  is  furnished  that  it  is 
applicable  to  them. 

I  have  been  totally  unable  to  find  satisfactory  European  re- 
sults in  regard  to  this  point.  The  English  works  can  furnish 
nothing,  both  on  account  of  the  lack  of  regulating  appliances 
and  because  the  monthly  bacterial  examinations  are  inadequate 
for  a  discussion  of  hourly  or  daily  changes.  The  results  from 


RATE   OF  FILTRATION  AND   LOSS   OF  HEAD.  65 

the  older  Continental  works  are  also  excluded  for  one  or  the 
other,  or  more  often  for  both,  of  the  above  reasons.  The  Ham- 
burg, Tegel,  and  Maggel  results,  so  far  as  they  go,  show  no  de- 
terioration with  increased  heads,  but  the  heads  are  limited  to  24 
or  28  inches  by  the  construction  of  the  filters,  and  the  results 
thus  entirely  fail  to  show  what  would  be  obtained  with  heads 
more  than  twice  as  high. 

I  am  thus  forced  to  conclude  that  there  is  no  adequate  evi- 
dence of  inferior  efficiency  with  high  heads  in  filters  where  the 
rates  are  independent  of  the  water-level  in  the  pure-water 
reservoir,  the  only  results  directly  to  the  point — the  Lawrence 
results  mentioned  above — indicating  that  the  full  efficiency  is 
maintained  with  heads  reaching  at  least  72  inches. 

The  principal  reason  for  desiring  to  allow  a  considerable  loss 
of  head  is  an  economical  one  ;  the  period  will  then  be  length- 
ened, while  the  frequency  of  scraping  and  the  volume  of  sand  to 
be  washed  and  replaced  will  be  correspondingly  reduced.  There 
may  be  other  advantages  in  long  periods,  such  as  less  trouble 
with  scraping  and  better  work  in  cold  winter  weather,  but  the 
cost  is  the  most  important  consideration. 

It  is  the  prevalent  idea  among  the  German  engineers  that 
the  loss  of  head  after  reaching  24  to  30  inches  would  increase 
very  rapidly,  so  that  the  quantity  of  water  filtered,  in  case  a 
much  higher  head  was  allowed,  would  not  be  materially  in- 
creased. No  careful  investigations,  however,  have  been  made, 
and  indeed  they  are  hardly  possible  with  existing  arrangements, 
as  in  the  older  filters  the  loss  of  head  fluctuates  with  varying 
rates  of  filtration  in  such  a  way  that  only  results  of  very  doubt- 
ful value  can  be  obtained,  and  in  the  newer  works  the  loss  of 
head  is  too  closely  limited,  and  the  curves  which  can  be  drawn 
by  extrapolation  are  evidently  no  safe  indications  of  what  would 
actually  happen  if  the  process  was  carried  farther. 

On  the  other  hand,  I  was  told  by  the  attendant  at  Darling- 
ton, England,  that  since  the  building  of  the  weir  a  few  years  ago, 


66  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

which  now  limits  the  loss  of  head  to  about  18  inches  instead  of 
the  5  feet  or  more  formerly  used,  the  quantity  of  sand  to  be  re- 
moved has  been  three  times  as  great  as  formerly.  No  records 
are  kept,  and  this  can  only  be  given  as  the  general  impression  of 
the  man  who  superintends  the  work. 

At  Lawrence  the  average  quantities  of  water  filtered  between 
scrapings  with  sand  of  an  effective  size  of  0.20  mm.  have  been  as 
follows : 

Maximum  Loss  of  Million  Gallons  per  Acre  filtered 

Head.  between  Scrapings. 

1892.  !893.          Average. 

70  inches 58     88     73 

34   "  32     22     27 

22    " 17       l6       l6 

With  sand  of  an  effective  size  of  0.29  mm.  the  results  were  : 

1893. 

70  inches 7° 

22       "     29 

These  results  indicate  a  great  increase  in  the  quantity  of  water 
filtered  between  scrapings  with  increasing  heads,  the  figures 
being  nearly  proportional  to  the  maximum  heads  used  in  the 
respective  cases.  It  is,  of  course,  quite  possible  that  the  results 
would  differ  in  different  places  with  the  character  of  the  raw 
water  and  of  the  filtering  material. 

The  depth  of  sand  to  be  removed  by  scraping  at  one  time  is, 
within  limits,  practically  independent  of  the  quantity  of  dirt 
which  it  has  accumulated,  and  any  lengthening  of  the  period 
means  a  corresponding  reduction  in  the  quantity  of  sand  to  be 
removed,  washed  and  replaced  and  consequently  an  important 
reduction  in  the  operating  cost,  as  well  as  a  reduction  in  the 
area  of  filters  out  of  use  while  being  cleaned,  and  so,  in  the 
capital  cost. 

Among  the  minor  objections  to  an  increased  loss  of  head  are 
the  greater  head  against  which  the  water  must  be  pumped,  and 


RATE   OF  FILTRATION  AND    LOSS   OF  HEAD.  7 

the  possible  increased  difficulty  of  filling  filters  with  filtered 
water  from  below  after  scraping,  but  these  would  hardly  have 
much  weight  against  the  economy  indicated  by  the  Lawrence 
experiments  for  the  higher  heads. 

High  heads  will  also  drive  an  increased  quantity  of  water 
through  any  cracks  or  passages  in  the  filter.  Such  leaks  have 
at  last  been  found  to  be  the  cause  of  the  inferior  work  of  the 
covered  filters  at  Stralau,  the  water  going  down  unfiltered  in 
certain  corners,  especially  at  high  heads;  but  with  careful  con- 
struction there  should  be  no  cracks,  and  with  the  aid  of  bac- 
teriology to  find  the  possible  leaks  this  ought  not  to  be  a  valid 
objection. 

In  conclusion :  the  trend  of  opinion  is  strongly  in  favor  of 
limiting  the  loss  of  head  to  about  24  to  30  inches  as  was  suggested 
by  Kirkwood,  but  I  am  forced  to  conclude  that  there  is  reason 
to  believe  that  equally  good  results  can  be  obtained  with  lower 
operating  expenses  by  allowing  higher  heads  to  be  used,  at  least 
in  the  case  of  filters  with  modern  regulating  appliances,  and, 
I  would  suggest  that  filters  should  be  built  so  as  not  to  exclude 
the  use  of  moderately  high  heads,  and  that  the  limit  to  be 
permanently  used  should  be  determined  by  actual  tests  of 
efficiency  and  length  of  period  with  various  losses  of  head  after 
starting  the  works. 


68  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


CHAPTER  V. 
CLEANING  FILTERS. 

WHEN  a  filter  has  become  so  far  clogged  that  it  will  no 
longer  pass  a  satisfactory  quantity  of  water  with  the  allowable 
head  it  must  be  cleaned  by  scraping  off  and  removing  the  upper 
layer  of  dirty  sand. 

To  do  this  without  unnecessary  loss  of  time  the  unfiltered 
water  standing  upon  the  filter  is  removed  by  a  drain  above  the 
sand  provided  for  that  purpose.  The  water  in  the  sand  must 
then  be  lowered  below  the  surface  of  the  sand  by  drawing  water 
from  the  underdrains  until  the  sand  is  firm  enough  to  bear  the 
weight  of  the  workmen.  By  the  time  that  this  is  accomplished 
the  last  water  on  the  surface  should  have  soaked  away,  and  the 
filter  is  ready  to  be  scraped.  This  is  done  by  workmen  with 
wide,  sharp  shovels,  and  the  sand  removed  is  taken  to  the  sand- 
washing  apparatus  to  be  washed  and  used  again.  Special  pains 
are  given  to  securing  rapid  and  cheap  transportation  of  the  sand. 
In  some  cases  it  is  wheeled  out  of  the  filter  on  an  inclined  plane 
to  the  washer.  In  other  cases  a  movable  crane  is  provided 
which  lifts  the  sand  in  special  receptacles  and  allows  it  to  fall 
into  cars  on  a  tram-line  on  which  the  crane  also  moves.  The 
cars  as  filled  are  run  to  the  washer  and  also  serve  to  bring 
back  the  washed  sand.  When  the  dirty  sand  has  been  removed, 
the  surface  of  the  sand  is  carefully  smoothed  and  raked.  This  is 
especially  necessary  to  remove  the  effects  of  the  workmen's 
boots. 

It  is  customary  in  the  most  carefully  managed  works  to  fill 
the  sand  with  filtered  water  from  below,  introduced  through  the 
underdrains.  In  case  the  ordinary  level  of  the  water  in  the 


CLEANING  FILTERS.  69 

pure-water  canal  is  higher  than  the  surface  of  the  sand  in  the 
filters,  this  is  accomplished  by  simply  opening  a  gate  provided 
for  the  purpose,  which  allows  the  water  to  pass  around  the 
regulating  apparatus.  Otherwise  filters  can  be  filled  from  a 
special  pipe  taking  its  water  from  any  filter  which  at  that  time 
can  deliver  its  effluent  high  enough  for  that  purpose.  The 
quantity  of  water  required  for  filling  the  sand  from  below  is 
ordinarily  but  a  fraction  of  one  per  cent  of  the  quantity  filtered. 

Formerly,  instead  of  filling  from  below,  after  cleaning,  the 
raw  water  was  brought  directly  onto  the  surface  of  the  filter. 
This  was  said  to  only  imperfectly  fill  the  sand-pores,  which 
still  contained  much  air.  If,  however,  the  water  is  not  brought 
on  too  rapidly  it  will  sink  into  the  sand  near  the  point  where  it 
is  applied,  pass  laterally  through  the  sand  or  underlying  gravel 
to  other  parts  of  the  filter,  and  then  rise,  so  that  even  in  this 
case  all  but  a  little  of  the  filter  will  be  really  filled  from  below. 
This  is,  however,  open  to  the  objection  that  however  slowly  the 
water  is  introduced,  the  sand  which  absorbs  it  around  the  inlet 
filters  it  at  a  very  high  rate  and  presumably  imperfectly,  so  that 
the  water  in  the  underdrains  at  the  start  will  be  poor  quality 
and  the  sand  around  the  inlet  will  be  unduly  clogged.  The 
practice  of  filling  from  below  is  therefore  well  founded. 

As  soon  as  the  surface  of  the  sand  is  covered  with  the  water 
from  below,  raw  water  is  introduced  from  above,  filling  the  filter 
to  the  standard  height,  care  being  taken  at  first  that  no  currents 
are  produced  which  might  wash  the  surface  of  the  sand.  It  has 
been  recommended  by  Piefke  and  others  that  this  water  should 
be  allowed  to  stand  for  a  time  up  to  twenty-four  hours  before 
starting  the  filtration,  to  allow  the  formation  of  a  sediment  layer, 
and  in  some  places,  especially  at  Berlin  and  the  works  of  some 
of  the  London  companies,  this  is  done ;  but  varying  importance 
is  attached  to  the  procedure,  and  it  is  invariably  omitted,  so  far 
as  I  can  learn,  when  the  demand  for  water  is  heavy. 

The  depth  of  sand  removed  by  scraping  must  at  least  equal 


70  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

the  depth  of  the  discolored  layer,  but  there  is  no  sharp  dividing 
line,  the  impurities  gradually  decreasing  from  the  surface  down- 
ward. Fig.  12  shows  the  relative  number  of  bacteria  found  in 
the  sand  at  various  depths  in  one  of  the  Lawrence  experimental 
filters,  and  is  a  representative  result,  although  the  actual  num- 
bers vary  at  different  times.  In  general  it  may  be  said  that  the 
bulk  of  the  sediment  is  retained  in  the  upper  quarter  inch,  but 
it  is  desirable  to  remove  also  the  less  dirty  sand  below  and,  in 
fact,  it  is  apparently  impossible  with  the  method  of  scraping  in 
use  to  remove  so  thin  a  layer  as  one  fourth  inch.  Practically 


"Bacteria  per  Gram. 

100000 500000 


___  JLaycrjemoyedJjy  Scraping 


FIG.  12. — DIAGRAM  SHOWING  ACCUMULATION  OF  BACTERIA  NEAR  THE  SURFACE 

OF  THE  SAND. 


the  depth  to  which  sand  is  removed  is  stated  to  be  from  0.40 
to  1.20  inch.  Exact  statistics  are  not  easily  obtained,  but  I  think 
that  2  centimeters  or  0.79  inch  may  be  safely  taken  as  about 
the  average  depth  usually  removed  in  European  filters,  and  it 
is  this  depth  which  is  indicated  on  Fig.  12. 

At  the  Lawrence  Experiment  Station,  the  depth  removed 
is  often  much  less  than  this,  and  depends  upon  the  size  of  grain 
of  the  sand  employed,  the  coarser  sands  requiring  to  be  more 
deeply  scraped  than  the  finer  ones.  The  method  of  scraping, 
however,  which  allows  the  removal  of  very  thin  sand  layers,  is 


CLEANING   FILTERS.  /I 

only  possible  because  of  the  small  size  of  the  filters,  and  as  it 
is  incapable  of  application  on  a  large  scale,  the  depths  thus 
removed  are  only  interesting  as  showing  the  results  which 
might  be  obtained  in  practice  with  a  more  perfect  method  of 
scraping. 

The  replacing  of  the  washed  sand  is  usually  delayed  until 
the  filter  has  been  scraped  quite  a  number  of  times — commonly 
for  a  year.  The  last  scraping  before  refilling  is  much  deeper 
than  usual,  because  the  sand  below  the  depth  of  the  ordinary 
scraping  is  somewhat  dirty,  and  might  cause  trouble  if  left  below  ' 
the  clean  sand. 

In  England  it  is  the  usual  if  not  the  universal  practice  to 
replace  the  washed  sand  at  the  bottom  between  the  old  sand 
and  the  gravel.  This  is  done  by  digging  up  the  entire  filter 
in  sections  about  six  feet  wide.  The  old  sand  in  the  first  section 
is  removed  clear  down  to  the  gravel,  and  the  depth  of  washed 
sand  which  is  to  be  replaced  is  put  in  its  place.  The  old  sand 
from  the  next  six-foot  section  is  then  shovelled  upon  the  first 
section  of  clean  sand,  and  its  place  is  in  turn  filled  with  fresh 
sand.  With  this  practice  the  workmen's  boots  are  likely  to 
disturb  the  gravel  each  year,  necessitating  a  thicker  layer  of  the 
upper  and  finest  grade  than  would  otherwise  be  required. 

In  Germany  this  is  also  sometimes  done,  but  more  frequently 
the  upper  layer  of  slightly  clogged  sand  below  the  regular  scrap- 
ing is  removed  as  far  as  the  slightest  discoloration  can  be  seen, 
perhaps  6  inches  deep.  The  sand  below  is  loosened  for  another  6 
inches  and  allowed  to  stand  dry,  if  possible,  for  some  days  ;  after- 
wards the  washed  sand  is  brought  on  and  placed  above.  The 
washed  sand  is  never  replaced  without  some  such  treatment,  be- 
cause the  slightly  clogged  sand  below  the  layer  removed  would 
act  as  if  finer  than  the  freshly  washed  sand,*  and  there  would  be 
a  tendency  to  sub-surface  clogging. 

*  Report  Mass.  State  Board  oi  Health  for  1891,  p.  438  ;    1892,  page  409. 


72  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

FREQUENCY    OF   SCRAPING. 

The  frequency  of  scraping  depends  upon  the  character  of 
the  raw  water,  the  thoroughness  of  the  preliminary  sedimenta- 
tion, the  grain-size  of  the  filter  sand,  the  rate  of  filtration,  and 
the  maximum  loss  of  head  allowed.  With  suitable  conditions 
the  period  between  scrapings  should  never  be  less  than  one 
week,  and  will  but  rarely  exceed  two  months.  Under  excep- 
tional conditions,  however,  periods  have  been  recorded  as  low 
as  one  day  and  as  high  as  one  hundred  and  ten  days.  Periods 
of  less  than  a  week's  duration  are  almost  conclusive  evidence 
that  something  is  radically  wrong,  and  the  periods  of  one  day 
mentioned  were  actually  accompanied  by  very  inadequate  filtra- 
tion. In  1892  the  average  periods  at  the  German  works  varied 
from  9.5  days  at  Stettin  (with  an  excessive  rate)  to  40  days  at 
Brunswick,  the  average  of  all  being  25  days.* 

The  quantity  of  water  per  acre  filtered  between  scrapings 
forms  the  most  convenient  basis  for  calculation.  The  effect  of 
rate  (page  49),  loss  of  head  (page  65),  and  size  of  sand  grain  (page 
32)  have  already  been  discussed,  and  it  will  suffice  to  say  here 
that  the  total  quantity  filtered  between  scrapings  is  apparently 
independent  of  the  rate  of  filtration,  but  varies  with  the  maxi- 
mum loss  of  head  and  with  the  grain-size  of  the  sand,  and 
apparently  nearly  in  proportion  to  them.  Eleven  German  filter- 
works  in  1892,  drawing  their  waters  from  rivers,  filtered  on  an 
average  51  million  gallons  of  water  per  acre  between  scrapings, 
the  single  results  ranging  from  28  at  Bremen  to  71  at  Stuttgart, 
while  Zurich,  drawing  its  water  from  a  lake  which  is  but  very 
rarely  turbid,  filtered  260  million  gallons  per  acre  between  scrap- 
ings. Unfortunately,  the  quantities  at  Berlin,  where  (in  1892 
two  thirds  and  now  all)  the  water  is  drawn  from  comparatively 
large  ponds  on  the  rivers,  are  not  available  for  comparison. 

At  London,  in  1884,  the  average  quantities  of  water  filtered 

*  Appendix  IV. 


CLEANING  FILTERS.  73 

between  scrapings  varied  from  43  to  136  million  gallons  per 
acre  with  the  different  companies,  averaging  85,  and  in  1892  the 
quantities  ranged  from  73  to  157,  averaging  90  million  gallons 
per  acre.  The  greater  quantity  filtered  at  London  may  be  due 
to  the  greater  sizes  of  the  sedimentation-basins,  which  for  all  the 
companies  together  hold  a  nine  days'  supply  at  London  against 
probably  less  than  one  day's  supply  for  the  German  works. 

There  is  little  information  available  in  regard  to  the  fre- 
quency of  scraping  with  water  drawn  from  impounding  reser- 
voirs. In  some  experiments  made  by  Mr.  FitzGerald  at  the 
Chestnut  Hill  reservoir,  Boston,  the  results  of  which  are  as  yet 
unpublished,  a  filter  with  sand  of  an  effective  size  of  only  .09 
mm.  averaged  58  million  gallons  per  acre  between  scrapings 
for  nine  periods,  the  rate  of  filtration  being  1.50  million  gallons 
per  acre  daily,  while  another  filter,  with  sand  of  an  effec- 
tive size  of  .18  mm.,  passed  an  average  of  93  million  gallons 
per  acre  for  ten  periods  at  the  same  rate.  These  experiments 
extended  through  all  seasons  of  the  year,  and  taking  into  ac- 
count the  comparative  fineness  of  the  sands  they  show  rather 
high  quantities  of  water  filtered  between  scrapings. 

The  quantity  of  water  filtered  between  scrapings  is  usually 
greatest  in  winter,  owing  to  the  smaller  quantity  of  sediment  in 
the  raw  water  at  this  season,  and  is  lowest  in  times  of  flood, 
regardless  of  season.  In  summer  the  quantity  is  often  reduced 
to  a  very  low  figure  in  waters  supporting  algae  growths,  es- 
pecially when  the  filters  are  not  covered.  Thus  at  Stralau  in 
1893  during  the  algae  period  the  quantity  was  reduced  to  14 
million  gallons  per  acre  for  open  filters,*  but  this  was  quite 
exceptional,  the  much-polluted,  though  comparatively  clear,, 
Spree  water  furnishing  unusually  favorable  conditions  for  the 
algae. 

*Piefke,  Zeitschrift  fur  Hygiene,  1894,  p.  177. 


74  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

QUANTITY   OF  SAND    TO   BE   REMOVED. 

In  regard  to  the  quantity  of  sand  to  be  removed  and  washed, 
if  we  take  the  average  result  given  above  for  the  German  works 
filtering  river-waters  of  51,000,000  gallons  per  acre  filtered  be- 
tween scrapings,  and  the  depth  of  sand  removed  at  two  centi- 
meters or  0.79  inch,  we  find  that  one  volume  of  sand  is  required  for 
every  2375  volumes  of  water  filtered,  or  2.10  cubic  yards  per 
million  gallons.  At  Bremen,  the  highest  average  result,  the 
quantity  would  be  3.80  yards,  and  at  Stralau  during  the  algae 
season  7.70  yards.  At  Zurich,  on  the  other  hand,  the  quantity  is 
only  0.41  yard,  and  at  London,  with  87,000,000  gallons  per  acre 
filtered  between  scrapings,  the  quantity  of  sand  washed  would 
be  1.24  yards  per  million  gallons  ;  assuming  always  that  the  layer 
removed  is  0.79  inch  thick. 

These  estimates  are  for  the  regular  scrapings  only,  and  do 
not  include  the  annual  deeper  scraping  before  replacing  the 
sand,  which  would  increase  them  by  about  one  third. 

WASTING   THE   EFFLUENTS   AFTER   SCRAPING. 

It  has  already  been  stated  that  an  important  part  of  the  fil- 
tration takes  place  in  the  sediment  layer  deposited  on  top  of  the 
sand  from  the  water.  When  this  layer  is  removed  by  scraping 
its  influence  is  temporarily  removed,  and  reduced  efficiency  of 
filtration  may  result.  The  significance  of  this  reduced  efficiency 
became  apparent  when  the  bacteria  in  the  water  were  studied  in 
their  relations  to  disease,  and  Piefke  suggested  *  that  the  first 
effluent  after  scraping  should  be  rejected  for  one  day  after 
ordinary  scrapings  and  for  one  week  after  replacing  the  sand. 
In  a  more  recent  paper  f  he  reduces  these  estimates  to  the 
first  million  gallons  of  water  per  acre  filtered  after  scraping 

*  Journal  fur  Gas-  und  Wasscrvtrsorgung,  1887,  p.  595. 
f  Ze itschrift  fur  Hygiene,  1894,   p.  172. 


CLEANING   FILTERS.  75 

for  open  and  twice  as  great  a  quantity  for  covered  filters, 
and  to  six  days  after  replacing  the  sand,  which  last  he  estimates 
will  occur  only  once  a  year.  Taking  the  quantity  of  water 
filtered  between  scrapings  at  13.9  million  gallons  per  acre,  the 
quantity  observed  at  Stralau  in  the  summer  of  1893,  he  finds 
that  it  is  necessary  to  waste  9  per  cent  of  the  total  quantity  of 
effluent  from  open  and  13.8  per  cent  of  that  from  covered  filters. 

The  eleven  German  water-works  *  filtering  river-waters, 
however,  filtered  on  an  average  51.0  instead  of  13.9  million  gal- 
lons per  acre  between  scrapings,  and  applying  Piefke's  figures  to 
them  the  quantities  of  water  to  be  wasted  would  be  only  about 
one  fourth  of  his  estimates  for  Stralau. 

The  rules  of  the  Imperial  Board  of  Health  f  require  that 
every  German  filter  shall  be  so  constructed  "  that  when  an  in- 
ferior effluent  results  it  can  be  disconnected  from  the  pure- 
water  pipes  and  the  filtrate  allowed  to  be  wasted."  The  drain- 
pipe for  removing  the  rejected  water  should  be  connected 
below  the  apparatus  for  regulating  the  rate  and  loss  of  head,  so 
that  the  filter  can  be  operated  exactly  as  usual,  and  the  effluent 
can  be  turned  back  to  the  pure-water  pipes  without  stopping  or 
changing  the  rate.  The  works  at  Berlin  and  at  Hamburg  con- 
form to  this  requirment,  and  most  of  the  older  German  works 
have  been  or  are  being  built  over  to  make  them  do  so. 

In  regard  to  the  extent  of  deterioration  after  scraping, 
Piefke's  experiments  have  always  shown  much  larger  numbers 
of  bacteria  both  of  the  ordinary  forms  and  of  special  applied 
forms  on  the  first  day  after  scraping,  the  numbers  frequently 
being  many  times  as  high  as  at  other  times. 

At  the  Lawrence  Experiment  Station  it  was  found  in  1892 
that  on  an  average  the  number  of  water  bacteria  was  increased  by 
70  per  cent  (continuous  filters  only)  for  the  three  days  following 
scraping,  while  B.prodigiosus  when  applied  was  increased  140  per 

*  Appendix  IV.  f  Appendix  I. 


76  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

cent,  the  increase  being  most  marked  where  the  depth  of  sand 
was  least,  and  with  the  highest  rate  of  nitration. 

The  same  tendency  was  found  in  1893,  when  the  increase  in 
the  water  bacteria  on  the  first  day  after  scraping  was  only  19 
per  cent  and  B.  prodigiosus  64  per  cent,  but  for  a  portion  of  the 
year  the  difference  was  greater,  averaging  132  and  262  per  cent, 
respectively.  These  differences  are  much  less  than  those  re- 
corded by  Piefke,  and  with  the  high  efficiencies  regularly  ob- 
tained at  Lawrence  they  would  hardly  justify  the  expensive 
practice  of  wasting  the  effluent. 

The  reduction  in  efficiency  following  scraping  is  much  less 
at  low  rates,  and  if  a  filter  is  started  at  much  less  than  its 
normal  rate  after  scraping,  and  then  gradually  increased  to  the 
standard  after  the  sediment  layer  is  formed,  the  poor  work  will 
be  largely  avoided.  Practically  this  is  done  at  Berlin  and  at 
Hamburg.  The  filters  are  started  at  a  fourth  or  less  of  the  usual 
rates  and  are  gradually  increased,  as  past  experience  with  bac- 
terial results  has  shown  it  can  be  safely  done,  and  the  effluent  is 
then  even  at  first  so  well  purified  that  it  need  not  be  wasted. 

Practically  in  building  new  filters  the  provision  of  a  suitable 
connection  for  wasting  the  effluents  into  the  drain  which  is 
necessary  for  emptying  them  involves  no  serious  expense  and 
should  be  provided,  but  it  may  be  questioned  how  often  it 
should  be  used  for  wasting  the  effluents.  If  the  raw  water  is  so 
bad  that  a  good  effluent  cannot  be  obtained  by  careful  manipula- 
tion even  just  after  scraping,  the  course  of  the  Berlin  authorities 
in  closing  the  Stralau  works  and  seeking  a  less  polluted  supplv 
would  seem  to  be  the  only  really  safe  procedure. 

SAND-WASHING. 

The  sand-washing  apparatus  is  an  important  part  of  most 
European  filtering  plants.  It  seldom  happens  that  a  natural  sand 
can  be  found  clean  enough  and  sufficiently  free  from  fine  par- 


CLEANING  A  FILTER,  EAST  LONDON. 


WASHING  DIRTY  SAND  WITH  HOSE,  ANTWERP. 

f  To  face  page  76.] 


CLEANING   FILTERS. 


77 


tides,  although  such  a  sand  was  found  and  used  for  the  Lawrence 
filter.  Most  of  the  sand  in  use  for  filtration  in  Europe  was 
originally  washed.  In  the  operation  of  the  niters  also,  sand- 
washing  is  used  for  the  dirty  sand,  which  can  then  be  used  over 
and  over  at  a  much  lower  cost  than  would  be  the  case  if  fresh 
sand  was  used  for  refilling.  The  methods  used  for  washing 
sand  at  the  different  works  present  a  great  variety  both  in  their 
details  and  in  the  underlying  principles.  Formerly  boxes  with 
double  perforated  bottoms  in  which  the  sand  was  placed  and 
stirred  by  a  man  as  water  from  below  rose  through  them,  and 
other  similar  arrangements  were  commonly  used,  but  they  are 
at  present  only  retained,  so  far  as  I  know,  in  some  of  the  smaller 
English  works.  The  cleansing  obtained  is  apparently  consider- 
ably  less  thorough  than  with  some  of  the  modern  devices. 


ELEVATION 


FIG.  13. — HOSE-WASHING  FOR  DIRTY  SAND. 

Hose-washing  is  used  in  London  by  the  South wark  and  Vaux- 
hall,  Lambeth  and  Chelsea  companies,  and  also  at  Antwerp. 
For  this  a  platform  is  constructed  about  15  feet  long  by  8  feet 
wide,  with  a  pitch  lengthwise  of  6  to  8  inches  (Fig.  13).  The 


78  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

platform  is  surrounded  by  a  wall  rising  from  one  foot  at  the  bottom 
to  three  feet  high  at  the  top,  except  the  lower  end,  which  is  closed 
by  a  removable  plank  weir  5  or  6  inches  high.  From  two  to 
four  cubic  yards  of  the  sand  are  placed  upon  this  platform  and  a 
stream  of  water  from  a  hose  with  a  f  or  {-inch  nozzle  is  played 
upon  it,  moving  it  about  from  place  to  place.  The  sand  itself 
is  always  kept  toward  the  upper  end  of  the  platform,  while  the 
water  writh  the  dirt  removed  flows  down  into  the  pond  made  by 
the  weir,  where  the  sand  settles  out  and  the  dirt  overflows  with 
the  water.  When  the  water  comes  off  clear,  which  is  usually 
after  an  hour  or  a  little  less,  the  weir  is  removed,  and,  after 
draining,  the  sand  is  removed.  These  arrangements  are  built  in 
pairs  so  that  the  hose  can  be  used  in  one  while  the  sand  is  being 
changed  in  the  other.  They  are  usually  built  of  brick  laid  in 
cement,  but  plank  and  iron  are  also  used.  The  corners  are 
sometimes  carried  out  square  as  in  the  figure,  but  are  more  often 
rounded.  The  washing  is  apparently  fairly  well  done. 

In  Germany  the  so-called  "  drum  "  washing-machine,  drawings 
of  which  have  been  several  times  published,*  has  come  to  be 
almost  universally  used.  It  consists  of  a  large  revolving  cylin- 
der, on  the  bottom  of  the  inside  of  which  the  sand  is  slowly 
pushed  up  toward  the  higher  end  by  endless  screw-blades  at- 
tached to  the  cylinder,  while  water  is  freely  played  upon  it  all 
the  way.  The  machine  requires  a  special  house  for  its  accommo- 
dation and  from  2  to  4  horse-power  for  its  operation.  It  washes 
from  2.5  to  4  yards  of  sand  per  hour  most  thoroughly,  with  a 
consumption  of  from  n  to  14  times  as  large  a  volume  of  water. 
The  apparatus  is  not  patented  or  made  for  sale,  but  full  plans 
can  be  easily  secured. 

A  machine  made  by  Samuel  Pegg  &  Sons,  Leicester,  Eng.r 
pushes  the  sand  up  a  slight  incline  down  which  water  flows.  It 
is  very  heavy  and  requires  power  to  operate  it.  The  patent  has 

*  Glaser's  Anna/en,  1886,  p.  48;  Zeit.  /.  Hygiene,  1889,  p.  128. 


CLEANING   FILTERS.  79 

expired.  A  machine  much  like  it  but  lighter  and  more  conven- 
ient and  moved  by  water-power  derived  from  the  water  used 
for  washing  instead  of  steam-power  is  used  at  Zurich  with 
good  results. 

In  Green  way's  machine  the  sand  is  forced  by  a  screw  through, 
a  long  narrow  cylinder  in  which  there  is  a  current  of  water  in 
the  opposite  direction.  The  power  required  is  furnished  by  a 
water-motor,  as  with  the  machine  at  Zurich.  The  apparatus  is 
mounted  on  wheels  and  is  portable ;  it  has  an  appliance  for 
piling  up  the  washed  sand  or  loading  it  onto  cars.  It  is 
patented  and  is  manufactured  by  James  Gibb  &  Co.,  London. 

Several  of  the  London  water  companies  are  now  using 
ejector  washers,  and  such  an  apparatus  has  been  placed  by  the 
side  of  the  "  drum  "  washers  at  Hamburg.  This  apparatus  was 
made  by  Korting  Brothers  in  Hannover,  and  combines  the 
ejectors  long  made  by  that  firm  with  hoppers  from  designs 
by  Mr.  Bryan,  engineer  of  the  East  London  Water  Company. 
An  apparatus  differing  from  this  only  in  the  shape  of  the 
ejectors  and  some  minor  details  has  been  patented  in  England, 
and  is  for  sale  by  Messrs.  Hunter,  Frazer  &  Goodman,  Bow, 
London. 

Both  of  these  forms  consist  of  a  series  of  conical  hoppers, 
Irom  the  bottom  of  each  of  which  the  sand  and  water  are  forced 
into  the  top  of  the  next  by  means  of  ejectors,  the  excess  of  dirty 
water  overflowing  from  the  top  of  each  hopper.  The  apparatus 
is  compact  and  not  likely  to  get  out  of  order,  but  is  not  portable. 
It  can  be  easily  arranged  to  take  the  sand  at  the  level  of  the 
ground,  or  even  lower  if  desired,  and  deliver  it  washed  at  some 
little  elevation,  thus  minimizing  hand-labor.  The  washing  is 
regular  and  thorough.  The  objection  most  frequently  raised 
against  its  use  is  the  quantity  of  water  required,  but  at 
Hamburg  I  was  informed  that  the  volume  of  water  required 
was  only  about  15  times  that  of  the  sand,  while  almost  as  much 
(13-14  volumes)  were  required  for  the  "drum"  washers,  and 


80  FILTRATION   OF  PUBLIC  WATER-SUPPLIES. 

the  saving  in  power  much  more  than  offset  the  extra  cost  for 
water. 

In  addition  to  the  above  processes  of  sand-washing,  Piefke's 
method  of  cleaning  without  scraping*  might  be  mentioned,  al- 
though as  yet  it  has  hardly  passed  the  experimental  stage,  and 
has  only  been  used  on  extremely  small  filters.  The  process  con- 
sists of  stirring  the  surface  sand  of  the  filter  with  u  waltzers  " 
while  a  thin  sheet  of  water  rapidly  flows  over  the  surface.  This 
arrangement  necessitates  a  special  construction  of  the  filters,  pro- 
viding for  rapidly  removing  the  unfiltered  water  from  the  sur- 
face, and  for  producing  a  regular  and  rapid  movement  of  a  thin 
sheet  of  water  over  the  surface.  In  the  little  filters  now  in  use, 
one  of  which  I  saw  in  a  brewery  in  Berlin,  the  cleaning  is  rapidly, 
cheaply,  and  apparently  well  done. 

In  washing  dirty  sand  it  is  obvious  that  any  small  sand-grains 
will  be  removed  with  the  dirt,  and  in  washing  new  sand  the  main 
object  is  to  remove  the  grains  below  a  certain  size.  It  is  also 
apparent  that  the  sizes  of  grains  which  will  and  those  which  will 
not  be  removed  are  dependent  upon  the  mechanical  arrange- 
ments of  the  washer,  as,  for  example,  with  the  ejectors,  upon  the 
sizes  of  the  hoppers,  and  the  quantity  of  water  passing  through 
them,  and  care  should  be  taken  to  make  them  correspond  with 
the  size  of  grain  selected  for  the  filter  sand.  This  can  only  be 
done  by  experiment,  as  no  results  are  available  on  this  point. 

In  some  places  filtered  water  is  used  for  sand-washing,  al- 
though this  seems  quite  unnecessary,  as  ordinary  river-water 
answers  very  well.  It  is,  however,  often  cheaper,  especially  in 
small  works,  to  use  the  filtered  water  from  the  mains  rather  than 
provide  a  separate  supply  for  the  washers. 

The  quantity  of  water  required  for  washing  may  be  esti- 
mated at  15  times  the  volume  of  the  sand  and  the  sand  as  0.04 
per  cent  of  the  volume  of  the  water  filtered  (page  74),  so  that 

*  Vierteljahresschrift  fur  offentliche  Gesundheitspflcge,  1891,  p.  59. 


CLEANING   FILTERS.  8  I 

0.6  per  cent  of  the  total  quantity  of  water  filtered  will  be  re- 
quired for  sand- wash  ing. 

The  cost  of  sand-washing  in  Germany  with  the  "  drum  " 
washers  is  said  to  be  from  14  to  20  cents  per  cubic  yard,  in- 
cluding labor,  power,  and  water.  In  America  the  water  would 
cost  no  more,  but  the  labor  would  be  perhaps  twice  as  dear. 
With  an  ejector  apparatus  I  should  estimate  the  cost  of 
washing  dirty  sand  as  follows :  The  sand  would  be  brought  and 
dumped  near  to  the  washer,  and  one  man  could  easily  feed  it  in, 
as  no  lifting  is  required.  Two  men  would  probably  be  re- 
quired to  shovel  the  washed  sand  into  barrows  or  carts  with 
the  present  arrangements,  but  I  think  with  a  little  ingenuity 
this  handling  could  be  made  easier. 

ESTIMATED   COST   OF   OPERATING   EJECTOR  WASHERS  9   HOURS. 

Wages  of  3  men  at  $2.00 $6.00 

110,000  gals,  water  (15  times  the  volume  of  sand) 
at  0.05  a  thousand  gals 5.50 

Total  cost  of  washing  36  cubic  yards $11.50 

or  32  cents  a  cubic  yard. 


The  cost  of  washing  new  sand  might  be  somewhat  less.  The 
other  costs  of  cleaning  filters,  scraping,  transporting,  and  re- 
placing the  sand  are  much  greater  than  the  washing  itself. 
Lindley  states  that  at  Warsaw  29  days'  labor  of  10  hours  for  one 
man  are  required  to  scrape  an  acre  of  filter  surface,  and  four 
times  as  much  for  the  annual  deep  scraping,  digging  up,  and 
replacing  the  sand.  The  first  expense  occurs  in  general 
monthly,  and  the  second  only  once  a  year.  At  other  places 
where  I  have  secured  corresponding  data  the  figures  range  from 
19  to  40  days'  labor  to  scrape  one  acre,  and  average  about  the 
same  as  Lindley  estimates. 

Under  some  conditions  sand-washing  does  not  pay,  and  in 


82  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

still  others  it  is  almost  impossible.  No  apparatus  has  yet  been 
devised  which  will  wash  the  dirt  out  of  the  fine  dune-sands  used 
in  Holland  without  washing  a  large  part  of  the  sand  itself  away, 
and  in  these  works  fresh  sand,  which  is  available  in  unlimited 
quantities  and  close  to  the  works,  is  always  used.  At  Breslau 
the  dirty  sand  is  sold  for  building  purposes  for  one  third  of  the 
price  paid  for  new  sand  dredged  from  the  river,  delivered  at  the 
works,  and  no  sand  is  ever  washed.  Budapest,  Warsaw,  and 
Rotterdam  also  use  fresh  river-sand  without  washing,  except  a 
very  crude  washing  to  remove  clay  at  Budapest. 


THEORY  AND   EFFICIENCY   OF  CONTINUOUS  FILTRATION.      83 


CHAPTER  VI. 

THEORY  AND  EFFICIENCY  OF  CONTINUOUS  FILTRATION. 

THE  first  filters  for  a  public  water-supply  were  built  by  James 
Simpson,  engineer  of  the  Chelsea  Water  Company  at  London 
in  1829.  They  were  apparently  intended  to  remove  dirt  from 
the  water  in  imitation  of  natural  processes,  and  without  any  very 
clear  conception  of  either  the  exact  extent  of  purification  or  the 
way  in  which  it  was  to  be  accomplished.  The  removal  of  tur- 
bid;ty  was  the  most  obvious  result,  and  a  clear  effluent  was  the 
single  test  of  the  efficiency  of  filtration,  as  it  remains  the  legal 
criterion  of  the  work  of  the  London  filters  even  to-day,  notwith- 
standing the  discovery  and  use  of  other  and  more  delicate  tests. 
The  invention  and  use  of  methods  for  determining  the  organic 
matters  in  water  by  Wanklyn  and  Frankland,  about  1870,  led  to 
the  discovery  that  the  proportion  of  organic  matters  removed  by 
filtration  was  disappointingly  low,  and  as,  at  the  time,  and  for 
many  years  afterward,  an  exaggerated  importance  was  given  to 
the  mere  quantities  of  organic  matters  in  water,  it  was  con- 
cluded that  filtration  had  only  a  limited  influence  upon  the 
healthfulness  of  the  filtered  water,  and  that  practically  as  much 
care  must  be  given  to  securing  an  unpolluted  water  as  would 
be  the  case  if  it  were  delivered  direct  without  filtration.  This 
theory,  although  not  confirmed  by  more  recent  investigation,  un- 
doubtedly has  had  a  good  influence  upon  the  English  works  by 
causing  the  selection  of  raw  waters  free  from  excessive  pollu- 
tions, and,  in  cases  like  the  London  supplies,  drawn  from  the 
Thames  and  the  Lea,  in  stimulating  a  most  jealous  care  of  the 
watersheds  and  the  purification  of  sewage  by  the  towns  upon 
them. 


1$4  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

It  was  only  after  the  discovery  of  the  bacteria  in  water  and 
their  relations  to  health  that  the  hygenic  significance  of  filtration 
commenced  to  be  really  understood.  Investigations  of  the  bac- 
teria in  the  waters  before  and  after  filtration  were  carried  out  at 
Berlin  by  Plagge  and  Proskower,  at  London  by  Dr.  Percy 
Frankland,  and  also  at  Zurich,  Altona,  and  on  a  smaller  scale 
at  other  places.  These  investigations  showed  that  the  bacteria 
were  mainly  removed  by  filtration,  the  numbers  in  the  effluents 
rarely  exceeding  two  or  three  per  cent  of  those  in  the  raw  water. 
This  gave  a  new  aspect  to  the  problem. 

It  was  further  observed,  especially  at  Berlin  and  Zurich,  that 
the  numbers  of  bacteria  in  effluents  were  apparently  quite  inde- 
pendent of  the  numbers  in  the  raw  water,  and  the  theory  was 
formed  that  all  of  the  bacteria  were  stopped  by  the  filters,  and 
that  those  found  in  the  effluents  were  the  result  of  contamination 
from  the  air  and  of  growths  in  the  underdrains.  The  logical 
conclusion  from  this  theory  was  that  filtered  water  was  quite 
suitable  for  drinking  regardless  of  the  pollution  of  its  source. 

It  was,  however,  found  that  the  numbers  of  bacteria  in  the 
effluents  were  higher  immediately  after  scraping  than  at  other 
times,  and  it  was  concluded  that  before  the  formation  of  the 
sediment  layer  some  bacteria  were  able  to  pass  the  sand,  and  it 
was  therefore  recommended  that  the  first  water  filtered  after 
scraping  should  be  rejected. 

Piefke  at  Berlin  gave  the  subject  careful  study,  and  came  to 
the  conclusion  that  it  was  almost  entirely  the  sediment  layer 
which  stopped  the  bacteria,  and  that  the  bacteria  themselves 
in  the  sediment  layer  formed  a  slimy  mass  which  completely 
intercepted  those  in  the  passing  water.  When  this  layer  was 
removed  by  scraping,  the  action  was  stopped  until  a  new  crop 
of  bacteria  had  accumulated.  In  support  of  this  idea  he  stated 
that  he  had  taken  ordinary  good  filter-sand  and  killed  the  bac- 
teria in  it  by  heating  it,  and  that  on  passing  water  through,  no 
purification  was  effected — in  fact,  the  effluent  contained  more 


THEORY  AND   EFFICIENCY  OF  CONTINUOUS  FILTRATION.      85 

bacteria  than  the  raw  water.  After  a  little,  bacteria  established 
themselves  in  the  sand,  and  then  the  usual  purification  was  ob- 
tained. Piefke  concluded  that  the  action  of  the  filter  was  a 
biological  one ;  that  simple  straining  was  quite  inadequate  to< 
produce  the  results  obtained ;  that  the  action  of  the  filter  was 
mainly  confined  to  the  sediment  layer,  and  that  the  depth  of  sand 
beyond  the  slight  depth  necessary  for  the  support  of  this  layer 
had  no  appreciable  influence  upon  the  results.  The  effect  of 
this  theory  is  still  seen  in  the  shallow  sand  layers  used  at  Berlin- 
and  some  other  German  works,  although  at  London  the  tendency 
is  rather  toward  thicker  sand  layers. 

Piefke's  deductions,  however,  are  not  entirely  supported  by 
his  data  as  we  understand  them  in  the  light  of  more  recent  in- 
vestigation. The  experiment  with  sterilized  sand  has  been  re- 
peatedly tried  at  the  Lawrence  Experiment  Station  with  results 
which  quite  agree  with  Piefke's,  but  it  has  also  been  found  that 
the  high  numbers,  often  many  times  as  high  as  in  the  raw  water, 
do  not  represent  bacteria  which  pass  in  the  ordinary  course  of 
filtration,  but  instead  enormous  growths  of  bacteria  throughout 
the  sand  supported  by  the  cooked  organic  matter  in  it.  It  has 
been  repeatedly  found  that  ordinary  sand  quite  incapable  of  sup- 
porting bacterial  growths,  after  heating  to  a  temperature  capable 
of  killing  the  bacteria  will  afterwards  furnish  the  food  for  most 
extraordinary  numbers.  A  filter  of  such  sand  may  stop  the  bac- 
teria of  the  passing  water  quite  as  effectually  as  any  other  filter, 
but  if  so,  the  fact  cannot  be  determined  without  recourse  to 
special  methods,  on  account  of  the  enormous  numbers  of  bacteria 
in  the  sand,  a  small  part  of  which  are  carried  forward  by  the 
passing  water,  and  completely  mask  the  normal  action  of  the 
filter. 

The  theory  that  all  or  practically  all  of  the  bacteria  are  inter- 
cepted by  the  sediment  layer,  and  that  those  in  the  effluent  are 
the  result  of  growths  in  the  sand  or  underdrains,  received  two 
hard  blows  in  1889  and  1891,  when  mild  epidemics  of  typhoid  fever 


86  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

followed  unusually  high  numbers  of  bacteria  in  the  effluents  at 
Altona  and  at  Stralau  in  Berlin,  with  good  evidence  in  each  case 
that  the  fever  was  directly  due  to  the  water.  Both  of  these  cases 
came  during,  and  as  the  result  of,  severe  winter  weather  with 
open  niters  and  under  conditions  which  are  now  recognized  as 
extremely  unfavorable  for  good  nitration. 

As  a  result  of  the  first  of  these  epidemics  a  series  of  experi- 
ments were  made  at  Stralau  by  Frankel  and  Piefke  in  1890. 
Small  filters  were  constructed,  and  water  passed  exactly  as  in  the 
ordinary  filters.  Bacteria  of  special  kinds  not  existing  in  the 
raw  water  or  effluents  were  then  applied,  and  the  presence  of  a 
very  small  fraction  of  them  in  the  effluents  demonstrated  beyond 
a  doubt  that  they  had  passed  through  the  filters  under  the 
ordinary  conditions  of  filtration.  These  experiments  were  after- 
wards repeated  by  Piefke  alone  under  somewhat  different  con- 
ditions with  similar  results.  The  numbers  of  bacteria  passing, 
although  large  enough  to  establish  the  point  that  some  do  pass, 
were  nevertheless  in  general  but  a  small  fraction  of  one  per  cent 
of  the  many  thousands  applied. 

This  method  of  testing  the  efficiency  of  filters  had  already 
been  used  quite  independently  by  Prof.  Sedgwick  at  the  Law- 
rence Experiment  Station  in  connection  with  the  purification  of 
sewage,  and  has  since  been  extensively  used  there  for  experi- 
ments with  water-filtration. 

Kiimmel  also  found  at  Altona  that  while  in  the  regular  samples 
for  bacterial  examination,  all  taken  at  the  same  time  in  the  day, 
there  was  no  apparent  connection  between  the  numbers  of  bac- 
teria in  the  raw  water  and  effluents,  by  taking  samples  at  frequent 
intervals  throughout  the  twenty-four  hours,  as  has  been  done  in 
a  more  recent  series  of  experiments,  and  allowing  for  the  time 
required  for  the  water  to  pass  the  filters,  a  well-marked  connec- 
tion was  found  to  exist  between  the  numbers  of  bacteria  in  the 
raw  water  and  in  the  effluents. 

The  subject  has  more  recently  been  studied  in  much  detail  at 


THEORY  AND    EFFICIENCY   OF  CONTINUOUS  FILTRATION.     8/ 

the  Lawrence  Experiment-  Station,  and  it  now  appears  that  the 
bacteria  in  the  effluent  from  a  filter  are  from  two  sources: 
directly  from  the  filtered  water,  and  from  the  lower  layers  of  the 
filter  and  underdrains.  Thus  we  may  say  : 

Bacteria  in  effluent  =  Bacteria  from  underdrains  +  — X  bacteria 

IOO 

in  raw  water, 
where  a  is  the  per  cent  of  bacteria  actually  passing  the  filter. 

Both  of  these  terms  depend  upon  a  whole  series  of  complex 
and  but  imperfectly  understood  conditions.  In  general  the  bac- 
teria from  the  underdrains  are  low  in  cold  winter  weather,  often 
almost  nil,  while  at  Lawrence  with  water  temperatures  of  70  to 
75  degrees,  and  over,  in  July  and  August,  the  numbers  from  this 
source  may  reach  200  or  300,  but  for  the  other  ten  months  of  the 
year  rarely  exceed  50  under  normal  conditions.  In  summer  espe- 
cially it  seems  to  be  greater  at  low  than  at  high  rates  of  filtration 


»2'5 

j,.5 
X 

« 
£0.5 


012        3      -4       56        7       8        910 

RATE  OF  FILTRATION  -  MILLION  GALLONS  PER  .ACRE.  DAILY. 

FIG.  14. — SHOWING   BACTERIA  SUPPOSED   TO   COME   THROUGH    FILTERS   AND  FROM 

THE  UNDERDRAINS. 

(although  a  high  rate  for  a  short  time  only  increases  it),  and  so 
varies  in  the  opposite  way  from  the  numbers  actually  passing 
the  filters.  This  subject  is  by  no  means  clearly  understood ;  it 
is  difficult,  almost  impossible,  to  separate  the  numbers  of  bacteria 
into  the  two  parts — those  which  come  directly  through  and  may 
be  dangerous,  and  those  which  have  other  origins  and  are  harmless. 
The  sketch,  Fig.  14,  is  drawn  to  represent  my  idea  of  the  way 
they  may  be  divided.  It  has  no  statistical  basis  whatever.  The 
light  unshaded  section  shows  the  percentage  number  of  bacteria 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

which  I  conceive  to  be  coming  through  a  filter  under  given  con- 
ditions  at  various  rates  of  filtration,  while  the  shaded  section 
above  represents  the  bacteria  from  other  sources,  and  the  upper 
line  represents  the  sum  of  the  two,  or  the  total  number  of  bac- 
teria in  the  effluent.  The  relative  importance  of  the  two  parts 
would  probably  vary  widely  with  various  conditions.  With  the 
conditions  indicated  by  the  sketch  the  number  of  bacteria  in  the 
effluent  is  almost  constant :  for  a  variation  of  only  from  1.4  to  2.5 
per  cent  of  the  number  applied  for  the  whole  range  is  not  a  wide 
fluctuation  for  bacterial  results,  but  the  number  in  the  lower  and 
dangerous  section  is  always  rapidly  increasing  with  increasing 
rate. 

This  theory  of  filtration  accounts  for  many  otherwise  per- 
plexing facts.  The  conclusion  reached  at  Zurich  and  elsewhere 
that  the  efficiency  of  filtration  is  independent  of  rate  may  be  ex- 
plained in  this  way.  This  is  especially  probable  at  Zurich,  where 
the  number  of  bacteria  in  the  raw  water  was  only  about  200, 
and  an  extremely  large  proportion  relatively  would  have  to  pass 
to  make  a  well-marked  impression  upon  the  total  number  in  the 
effluent. 

These  underdrain  bacteria  are,  so  far  as  we  know,  entirely 
harmless ;  we  are  only  interested  in  them  to  determine  how  far 
they  are  capable  of  decreasing  the  apparent  efficiency  of  filtra- 
tion below  the  actual  efficiency,  or  the  per  cent  of  bacteria  really 
removed  by  the  filter. 

This  efficiency  is  dependent  upon  a  large  number  of  con- 
ditions many  of  which  have  already  been  discussed  in  connec- 
tion with  grain-size  of  filter  sand,  underdrains,  rate  of  filtration, 
loss  of  head,  etc.,  and  a  mere  reference  to  them  here  will  suffice. 
Perhaps  the  most  important  single  condition  is  the  rate,  the 
numbers  of  bacteria  passing  increase  rapidly  with  it.  Next,  fine 
sand  and  in  moderately  deep  layers  tends  to  give  high  efficiency. 
The  influence  of  the  loss  of  head,  often  mentioned,  is  not  shown 
to  be  important  by  the  Lawrence  results,  nor  can  I  find 


THEORY  AND   EFFICIENCY  OF  CONTINUOUS  FILTRATION.      89 

satisfactory  European  results  in  support  of  it.  Uniformity  in  the 
rate  of  nitration  on  all  parts  of  the  filtering  area  and  a  constant 
rate  throughout  the  twenty-four  hours  are  regarded  as  essential 
conditions  for  the  best  results.  Severe  winter  weather  has  in- 
directly, by  disturbing  the  regular  action  of  open  filters,  an  in- 
jurious influence,  and  has  been  the  cause  of  most  of  the  cases 
where  filtered  waters  have  been  known  to  injure  the  health  of 
those  who  have  drunk  them.  This  action  is  excluded  in  filters 
covered  with  masonry  arches  and  soil,  and  such  construction  is 
apparently  necessary  for  the  best  results  in  places  subject  to  cold 
winters. 

The  efficiency  of  filtration  under  various  conditions  has  been 
studied  by  a  most  elaborate  series  of  experiments  at  Lawrence 
with  small  filters  to  which  water  has  been  applied  containing  a 
bacterium  (B.  prodigiosus)  which  does  not  occur  naturally  in  this 
country  and  is  not  capable  of  growing  in  the  filter,  so  that  the 
results  should  represent  only  the  bacteria  coming  through  the 
filter  and  not  include  any  additions  from  the  underdrains.  These 
results,  which  have  been  published  in  full  in  the  reports  of  the 
Massachusetts  State  Board  of  Health,  especially  for  the  years 
1892  and  1893,  show  that  the  number  of  bacteria  passing  increases 
rapidly  with  increasing  rate,  and  slowly  with  decreasing  sand 
thickness  and  increased  size  of  sand-grain. 

Assuming  that  the  number  of  bacteria  passing  is  expressed 

by  the  formula 

1  (rate)'  X  effective  size  of  sand 
Per  cent  bacteria  passing  =  - 

2  vthickness  of  the  sand  in  inches 

where  the  rate  is  expressed  in  million  gallons  per  acre  daily,  and 
calculating  by  it  the  numbers  of  bacteria  for  the  seventy-three 
months  for  which  satisfactory  data  are  available  from  1 1  filters 
in  1892  and  1893,  \ve  find  that 
In  14  cases  the  numbers  observed  were  4  to  9  times  as  great  as 

the  calculated  numbers ; 
In  6  cases  they  were  2  to  3  times  as  great; 


90  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

In  35  cases   they   were  between   \  and   2   times  the  calculated 

numbers. 

In  17  cases  they  were  £  to  \  of  them. 
In  1 1  cases  they  were  less  than  \  the  calculated  numbers. 

The  agreement  is  only  moderately  good,  and  in  fact  no  such 
formula  could  be  expected  to  give  more  than  very  rough  approxi- 
mations, because  it  does  not  take  into  consideration  the  numerous 
other  elements,  such  as  uniformity  and  regularity  of  filtration, 
the  influence  of  scraping,  the  character  of  the  sediment  in  the 
raw  water,  etc.,  which  are  known  to  affect  the  results.  Perhaps 
the  most  marked  general  difference  is  the  tendency  of  new  or 
freshly-filled  filters  to  give  higher,  and  of  old  and  well-com- 
pacted filters  to  give  lower,  results  than  those  indicated  by  the 
formula. 

Comparing  this  formula  with  Piefke's  results  given  in  his 
"  Neue  Ermittelungen  "  k  the  formula  gives  in  the  first  series 
(0.34  mm.  sand,  0.50  m.  thick,  and  rate  100  mm.  per  hour),  0,25 
per  cent  passing,  while  the  average  number  of  B.  violations 
reported,  excluding  the  first  day  of  decreased  efficiency  after 
scraping,  was  0.26  per  cent.  In  the  second  series,  with  half  as 
high  a  rate  the  numbers  checked  exactly  the  calculated  0.06  per 
cent. 

In  other  experiments,!  however,  in  1893,  when  the  calculated 
per  cent  was  also  0.25,  only  0.03,  0.04,  and  0.07  per  cent  were 
observed  in  the  effluents. 

Comparing  the  results  from  the  actual  filters,  (which  numbers 
also  include  the  bacteria  from  the  underdrains  and  should  there- 
fore be  somewhat  higher)  with  the  numbers  calculated  as  pass- 
ing through,  I  find  that  for  the  46  days,  Aug.  20  to  Oct.  4, 
1893,  for  which  detailed  results  of  the  Stralau  works  are  given 
by  Piefke,  the  average  calculated  number  passing  is  0.20  per 


*  Journal  fur  Gas-  und  Wasserversorgung,  1891,  108. 
\  Zeitschrift  fur  Hygiene,  1894,  182. 


THEORY  AND   EFFICIENCY  OF  CONTINUOUS  FILTRATION.     91 

cent,  while  twice  as  many  were  observed  in  the  effluents ;  al- 
though three  of  the  niters  gave  better  effluents  than  the  other 
eight,  and  the  numbers  from  them  approximated  closely  the 
calculated  numbers.  If  we  calculate  the  percentages  of  bacteria 
passing  a  number  of  niters,  using  the  maximum  rate  of  nitration 
allowed  for  the  German  niters  where  this  is  accurately  deter- 
mined, and  for  the  English  niters  taking  the  maximum  rate  at 
one  and  one-half  times  the  rate  obtained  by  dividing  the  daily 
quantity  by  the  area  of  niters  actually  in  use,  we  obtain : 


Average 
Depth  of 
Sand, 
Inches. 

Effective 
Size  of 
Sand- 
grain. 

Maximum 
Rate  of 
Filtration. 

Per  cent 
Bac  teria 
passing 
i     r*d 

~  *  ^sand 

32 

O    31 

I    60 

o  07 

28 

O   34 

2    C7 

O   21 

Berlin,  Stralau  

2O 

O   34 

2    57 

O   25 

Miiggel 

2O 

O   34 

2    17 

O    21 

"      Tegel         

2O 

O   37 

2    C7 

O   27 

London,  Southwark  &  Vauxhall  

36 

O   34 

2    8l 

O   22 

West  Middlesex 

•3Q 

O    37 

2    8l 

O    "*3 

C4 

o  36 

3    27 

o  26 

-JO 

o  40 

3    27 

O    30 

"        Lambeth  

36 

o  36 

3   75 

O   42 

Middlesborou°rh                   ..        

2O 

O   42 

j-  /  j 

;  8; 

I     18 

Zurich                    ...          .... 

26 

O    3? 

j  'W3 

7    CQ 

I    QO 

The  numbers  actually  observed  are  in  every  case  higher  than 
the  calculated  per  cents  passing,  as  indeed  they  should  be  on 
account  of  those  coming  from  the  underdrains,  accidental  con- 
tamination of  the  samples,  etc. 

It  may  be  said  that  filtration  as  now  practised  in  European 
works  under  ordinary  conditions  never  allows  over  i  or  2  per 
cent  of  the  bacteria  of  the  raw  water  to  pass,  and  ordinarily  not 
over  one  fourth  to  one  half  of  one  per  cent,  although  exact  data 
cannot  be  obtained  owing  to  masking  effect  of  the  bacteria 
which  come  in  from  below  and  which  bear  no  relation  to  those 
of  the  raw  water.  By  increasing  the  size  of  filters,  fineness  and 


92  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

depth  of  sand  (as  at  Hamburg),  the  efficiency  can  be  materially 
increased  above  these  figures.  At  the  same  time  it  must  be 
borne  in  mind  that  the  effectiveness  of  a  filter  may  be  greatly 
impaired  by  inadequate  underdraining,  by  fluctuating  rates  of 
filtration  where  these  are  allowed,  by  freezing  in  winter  in  the 
case  of  open  filters  in  cold  climates,  and  by  other  irregularities, 
all  of  which  can  be  prevented  by  careful  attention  to  the 
respective  points. 

The  action  of  a  continuous  filter  throughout  is  mainly  that  of 
an  exceedingly  fine  strainer,  and  like  a  strainer  is  mainly  con- 
fined to  the  suspended  or  insoluble  matters  in  the  raw  water. 
The  turbidity,  sediment,  and  bacteria  of  the  raw  water  are 
largely  or  entirely  removed,  while  hardness,  organic  matter, 
and  color,  so  far  as  they  are  in  solution,  are  removed  to  only  a 
slight  extent,  if  at  all.  Hardness  can  be  removed  by  the  addi- 
tion of  lime  in  carefully  determined  quantity  before  filtration 
(Clark's  process),  by  means  of  which  the  excess  of  carbonic  acid 
in  the  water  is  absorbed  and  the  lime  added,  together  with  that 
previously  in  the  water,  is  precipitated. 

Ordinary  filtration  will  remove  from  one  fourth  to  one  third 
of  the  yellow-brown  color  of  peaty  water.  A  larger  proportion 
can  be  removed  by  the  addition  of  alum,  which  by  decomposing 
forms  an  insoluble  compound  of  alumina  with  the  coloring 
matter,  while  the  acid  of  the  alum  goes  into  the  effluent  either  as 
free  acid,  or  in  combination  with  the  lime  or  other  base  in  the 
water,  according  to  their  respective  quantities.  Freshly  pre- 
cipitated alumina  can  be  substituted  for  the  alum  at  increased 
expense  and  trouble,  and  tends  to  remove  the  color  without 
adding  acid  to  the  water.  These  will  be  discussed  more  in. 
detail  in  connection  with  mechanical  filters.  Alum  is  but  rarely 
used  in  slow  sand  filtration,  the  most  important  works  where  it 
is  used  being  in  Holland  with  peaty  waters.. 

After  all,  the  most  conclusive  test  of  the  efficiency  of  nitration 
is  the  healthfulness  of  the  people  who  drink  the  filtered  water ; 


THEORY  AN&    EFFICIENCY,  OF  CONTINUOUS  FILTRATION.      93 

and  the  fact  that  many  European  cities  take  water-supplies  from 
sources  which  would  not  be  considered  fit  for  use  in  the  United 
States  and,  after  filtering  them,  deliver  them  to  populations  having 
death-rates  from  water-carried  diseases  which  are  so  low  as  to  be 
the  objects  of  our  admiration,  is  the  best  proof  of  the  efficiency 
of  carefully  conducted  filtration. 

It  is  only  necessary  to  refer  to  London,  drawing  its  water 
from  the  two  small  and  polluted  rivers,  the  Thames  and  the  Lea; 
to  Altona,  drawing  its  water  from  the  Elbe,  polluted  by  the 
sewage  of  6,000,000  people,  700,000  of  them  within  ten  miles  above 
the  intakes  ;  to  Berlin,  using  the  waters  of  the  Havel  and  the 
Spree ;  to  Breslau,  taking  its  water  from  the  Oder  charged  with 
the  sewage  of  mining  districts  in  Silicia  and  Galicia,  where 
cholera  is  so  common ;  to  Lawrence,  with  its  greatly  decreased 
death-rate  since  it  has  had  filtered  water,  and  to  the  hundred 
other  places  which  protect  themselves  from  the  infectious  mat- 
ters in  their  raw  waters  by  means  of  filtration.  A  few  of  these 
cases  are  described  more  in  detail  in  Appendices  V  to  IX,  and 
many  others  in  the  literature  mentioned  in  Appendix  X. 

An  adequate  presentation  of  even  those  data  which  have  been 
already  worked  up  and  published  would  occupy  too  much 
space.  I  think  every  one  who  has  carefully  studied  the  recent 
history  of  water  filtration  in  its  relation  to  disease  has  been 
convinced  that  filtration  carefully  executed  under  suitable  and 
normal  conditions,  even  if  not  an  absolute,  is  at  least  a  very 
substantial  protection  against  water-carried  diseases,  and  the  few 
apparent  failures  to  remove  objectionable  qualities  have  been 
without  exception  due  to  abnormal  conditions  which  are  now 
understood  and  in  future  can  be  prevented. 

BACTERIAL   EXAMINATION  OF  WATERS. 

Every  large  filter-plant  should  have  arrangements  for  the 
systematic  bacterial  examination  of  the  water  before  and  after 


94  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

filtration,  especially  where  the  raw  water  is  subject  to  serious 
pollution.  Such  examinations  need  not  be  excessively  expensive, 
and  they  will  not  only  show  the  efficiency  of  the  plant  as  a  whole, 
but  may  be  made  to  show  the  relative  efficiencies  of  the  separate 
filters,  the  relative  efficiencies  at  different  parts  of  the  periods  of 
operation,  the  effect  of  cold  weather,  etc.,  and  will  then  be  a  sub- 
stantial aid  to  the  superintendent  in  always  securing  good 
effluents  at  the  minimum  cost. 

In  addition  a  complete  record  of  the  bacteria  in  the  water  at 
different  times  may  aid  in  determining  definitely  whether  the 
water  was  connected  with  outbreaks  of  disease.  Thus  if  an  out- 
break of  disease  of  any  kind  were  preceded  at  a  certain  interval 
by  a  great  increase  in  the  number  of  bacteria, — as  has  been  the 
case,  for  example,  with  the  typhoid  epidemics  at  Altona  and 
Berlin  (see  Appendices  II  and  VII), — a  presumption  would  arise 
that  they  might  have  been  connected  with  each  other,  and  each 
time  it  was  repeated  the  presumption  would  be  strengthened,, 
while,  on  the  other  hand,  outbreaks  occurring  while  the  bacteria 
remained  constantly  low  would  tend  to  discredit  such  a  theory. 

Bacterial,  investigations  inaugurated  after  an  epidemic  is 
recognized,  as  has  frequently  been  done,  seldom  lead  to  results 
of  value,  both  because  the  local  normal  bacterial  conditions  are 
generally  unknown  at  the  commencement  of  the  investigation, 
and  because  the  most  important  time,  the  time  of  infection,  is 
already  long  past  before  the  first  samples  are  taken.  The  fact 
that  such  sporadic  activities  have  led  to  few  definite  results, 
should  throw  no  discredit  upon  continued  observations,  which 
have  repeatedly  proved  of  inestimable  value. 

Considerable  misconception  of  the  use  of  bacterial  examina- 
tions exists.  The  simple  bacterial  count  ordinarily  used,  and  of 
which  I  am  now  speaking,  does  not  and  cannot  show  whether  a 
water  contains  disease-germs  or  not.  I  object  to  the  Chicago 
water,  not  so  much  because  a  glass  of  it  contains  a  hundred  thou- 
sand bacteria  more  or  less,  as  because  I  am  convinced,  by  a  study 


THEORY  AND   EFFICIENCY   OF  CONTINUOUS  FILTRATION.      95 

of  its  source  in  connection  with  the  city's  death-rate,  that  it  actu- 
ally carries  disease-germs  which  prove  injurious  to  thousands 
of  those  who  drink  it.  Now  the  fact  being  admitted  that  the 
water  is  injurious  to  health,  variations  in  the  numbers  of  bacteria 
in  the  water  drawn  from  different  intakes  and  at  different  times 
probably  correspond  roughly  with  varying  proportions  of  fresh 
sewage,  and  indicate  roughly  the  relative  dangers  from  the  use 
of  the  respective  waters.  If  niters  should  be  introduced,  the 
numbers  of  bacteria  in  the  effluents  under  various  conditions 
would  be  an  index  of  the  respective  efficiencies  of  nitration,  and 
would  serve  to  detect  poor  work,  and  would  probably  suggest 
the  measures  necessary  for  better  results. 

I  would  suggest  the  desirability  of  such  investigations  where 
mechanical  niters  are  used,  quite  as  much  as  in  connection  with 
slow  nitration ;  and  it  would  also  be  most  desirable  in  the  case  of 
many  water-supplies  which  are  not  filtered  at  all.  Such  con- 
tinued observations  have  been  made  at  Berlin  since  1884;  at 
London  since  1886;  at  Boston  and  Lawrence  since  1888;  and 
recently  at  a  large  number  of  places,  including  Chicago,  where 
observations  by  the  city  were  commenced  in  1894.  They  are  now 
required  by  the  German  Government  in  the  case  of  all  filtered 
public  water-supplies  in  Germany,  without  regard  to  the  source 
of  the  raw  water.  The  German  standard  requires  that  the  efflu- 
ent from  each  single  filter,  as  well  as  the  mixed  effluent  and  raw 
water,  shall  be  examined  daily,  making  at  some  works  10  to  30 
samples  daily.  This  amount  of  work,  however,  can  usually  be 
done  by  a  single  man  ;  and  when  a  laboratory  is  once  started,  the 
cost  of  examining  20  samples  a  day  will  not  be  much  greater 
than  if  only  20  a  week  are  taken.  In  England  and  at  some  of 
the  Continental  works  drawing  their  waters  from  but  slightly 
polluted  sources,  much  smaller  numbers  of  samples  are  examined. 

The  question  whether  the  examinations  should  be  made  under 
the  direction  of  the  water-works  company  or  department,  or  by 
an  independent  body — as,  for  instance,  by  the  Board  of  Health— 


^6  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

will  depend  upon  local  conditions.  The  former  arrangement 
gives  the  superintendent  of  the  filters  the  best  chance  to  study 
their  action,  as  he  can  himself  control  the  collection  of  samples 
in  connection  with  the  operation  of  the  filters,  and  arrange  them 
to  throw  light  upon  the  points  he  wishes  to  investigate ;  while 
•examination  by  a  separate  authority  affords  perhaps  greater 
protection  against  the  possible  carelessness  or  dishonesty  of 
water-works  officials.  An  arrangement  being  adopted  in  many 
cases  in  Germany  is  to  have  a  bacterial  laboratory  at  the  works 
which  is  under  the  control  of  the  superintendent,  and  in  which 
the  very  numerous  compulsory  observations  are  made,  while  the 
Board  of  Health  causes  to  be  examined  from  time  to  time  by 
its  own  representatives,  who  have  no  connection  with  the  water- 
works, samples  taken  to  check  the  water-works  figures,  as  well 
as  to  show  the  character  of  the  water  delivered. 

It  seems  quite  desirable  to  have  a  man  whose  principal  busi- 
ness is  to  make  these  examinations ;  as  in  case  he  also  has  numer- 
ous other  duties,  the  examinations  may  be  found  to  have  been 
neglected  at  some  time  when  they  are  most  wanted.  Such  a 
man  should  have  had  thorough  training  in  the  principles  of  bac- 
terial manipulation,  but  it  is  quite  unnecessary  that  he  should  be 
an  expert  bacteriologist,  especially  if  a  competent  bacteriologist 
is  retained  for  consultation  in  cases  of  doubt  or  difficulty. 


INTERMITTENT  FIL  TRA  TION.  97 


CHAPTER  VII. 
INTERMITTENT   FILTRATION. 

BY  intermittent  filtration  is  understood  that  filtration  in 
which  the  filtering  material  is  systematically  and  adequately 
ventilated,  and  where  the  water  during  the  course  of  filtration  is 
brought  in  contact  with  air  in  the  pores  of  the  sand.  In  con- 
tinuous filtration,  which  alone  has  been  previously  considered, 
the  air  is  driven  out  of  the  sand  as  completely  as  possible  before 
the  commencement  of  filtration,  and  the  sand  is  kept  continu- 
ously covered  with  water  until  the  sand  becomes  clogged  and  a 
draining,  with  an  incidental  aeration,  is  necessary  to  allow  the 
filter  to  be  scraped  and  again  put  in  service. 

In  intermittent  filtration,  on  the  other  hand,  water  is  taken 
over  the  top  of  the  drained  sand  and  settles  into  it,  coming  in 
contact  with  the  air  in  the  pores  of  the  sand,  and  passes  freely 
through  to  the  bottom  when  the  water-level  is  kept  well  down. 
After  a  limited  time  the  application  of  water  is  stopped,  and  the 
filter  is  allowed  to  again  drain  and  become  thoroughly  aerated 
preparatory  to  receiving  another  dose  of  water. 

This  system  of  treating  water  was  suggested  by  the  un- 
equalled purification  of  sewage  effected  by  a  similar  treatment. 
It  has  been  investigated  at  the  Lawrence  Experiment  Station, 
and  applied  to  the  construction  of  a  filter  for  the  city  of  Law- 
rence, both  of  which  are  due  to  the  indefatigable  energy  of 
Hiram  F.  Mills,  C.E. 

In  its  operation  intermittent  differs  from  continuous  filtration 
in  that  the  straining  action  is  less  perfect,  because  the  filters 
yield  no  water  while  being  aerated,  and  must  therefore  filter  at  a 
greater  velocity  when  in  use  to  yield  the  same  quantity  of  water 
in  a  given  time,  and  also  on  account  of  the  mechanical  disturb- 


98  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

ance  which  is  almost  invariably  caused  by  the  application  of  the 
water ;  but,  on  the  other  hand,  the  oxidizing  powers  of  the  filter, 
or  the  tendency  to  nitrify  and  destroy  the  organic  matters,  are 
stronger,  and  in  addition,  if  the  rate  is  not  too  high,  the  bacteria 
die  more  rapidly  in  the  thoroughly  aerated  sand  than  is  the  case 
with  ordinary  filters. 

It  was  found  at  Lawrence  in  connection  with  sewage  filters 
that  when  nitrification  was  actively  taking  place  the  numbers  of 
bacteria  were  much  lower  than  under  opposite  conditions,  and  it 
was  thought  that  nitrification  in  itself  might  cause  the  death  of 
the  bacteria.  Later  experiments,  however,  with  pure  cultures 
of  bacteria  of  various  kinds  applied  to  intermittent  filters 
with  water  to  which  ammonia  and  salts  suitable  for  nitrification 
were  added,  showed  that  bacteria  of  all  the  species  tried  were 
able  to  pass  the  filter  in  the  presence  of  nitrification,  producing 
at  least  one  thousand  times  as  much  nitrates  as  could  result  in 
any  case  of  water-filtration,  as  freely  as  was  the  case  when  the 
ammonia  was  not  added  and  there  was  but  little  nitrification. 
These  results  showed  conclusively  that  nitrification  in  itself  is 
not  an  important  factor  in  bacterial  removal,  although  nitrifica- 
tion and  bacterial  purification  do  to  some  extent  go  together ; 
perhaps  in  part  because  the  nitrification  destroys  the  food  of 
the  bacteria  and  so  starves  them  out,  but  probably  much  more 
because  the  conditions  of  aeration,  temperature,  etc.,  which 
favor  nitrification  also  favor  equally,  and  even  in  its  absence, 
the  death  of  the  bacteria. 

The  rate  at  which  water  must  pass  through  an  intermittent 
filter  is,  on  account  of  the  intervals  of  rest,  considerably  greater 
than  that  required  to  give  a  corresponding  total  yield  from  a 
continuous  filter,  and  its  straining  effect  is  reduced  to  an  extent 
comparable  to  this  increase  in  rate  ;  and  if  other  conditions  did 
not  come  in,  the  bacterial  efficiency  of  an  intermittent  filter 
would  remain  below  that  of  a  continuous  one. 

As  a  matter  of  fact  the  bacterial  efficiency  has  usually  been 


INTERMITTENT  FILTRATION.  99 

found  to  be  less  with  intermittent  filters  at  the  Lawrence  Ex- 
periment Station,  when  they  have  been  run  at  rates  such  as  are 
commonly  used  for  continuous  filters  in  Europe,  say  from  one 
and  one  half  to  two  million  gallons  and  upwards  per  acre  daily. 
With  lower  rates,  and  especially  with  rather  fine  materials,  the 
bacterial  efficiency  is  much  greater;  but  it  may  be  doubted 
whether  it  would  ever  be  greater  than  that  of  a  continuous  filter 
with  the  same  filtering  material  and  the  same  total  yield  per 
acre.  The  number  of  bacteria  coming  from  the  underdrains 
is  apparently  generally  less,  and  with  very  high  summer  tem- 
peratures much  less,  than  in  continuous  filters,  and  this  often 
gives  an  apparent  bacterial  superiority  to  the  intermittent  filters. 

The  effluents  from  intermittent  often  contain  less  slightly  or- 
ganic matter  than  those  from  continuous  filters  ;  but,  on  the  other 
hand,  hardly  any  water  proposed  for  a  public  water-supply  has 
organic  matter  enough  to  be  of  any  sanitary  significance  what- 
ever, apart  from  the  living  bodies  which  often  accompany  it; 
and  if  the  latter  are  removed  by  straining  or  otherwise,  we  can 
safely  disregard  the  organic  matters.  In  addition,  the  water 
filtered  will  in  a  great  majority  of  cases  have  enough  air  dis- 
solved in  itself  to  produce  whatever  oxidation  there  is  time  fo* 
in  the  few  hours  required  for  it  to  pass  the  filter,  and  it  is  only 
at  very  low  rates  of  filtration  that  intermittent  filters  produce 
effluents  of  greater  chemical  purity  than  by  the  ordinary  process. 
The  yellow-brown  coloring  matter  present  in  so  many  waters 
appears  to  be  quite  incapable  of  rapid  nitrification  ;  and  where  it 
is  to  some  extent  removed  by  filtration,  the  action  is  dependent 
upon  other  and  but  imperfectly  understood  causes  which  seem 
to  act  equally  in  continuous  and  intermittent  filters. 

The  peculiarities  of  construction  involved  by  this  method  of 
filtration  will  be  best  illustrated  by  a  discussion  of  the  Lawrence 
city  filter  designed  by  Hiram  F.  Mills,  C.E.,  which  is  the  only 
filter  in  existence  upon  this  plan.* 

*  I  am  informed  that  several  other  filters  upon  the  same  principle  have  been  more 
recently  built. 


100  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


THE   LAWRENCE  FILTER. 

The  filter  consists  of  a  single  bed  2^  acres  in  area,  the  bot- 
tom of  which  is  7  feet  below  low  water  in  the  river,  and  filled 
with  gravel  and  sand  to  an  average  depth  of  4^  feet.  The  filter 
is  all  in  a  single  bed  instead  of  being  divided  into  the  three  or 
ifour  sections  which  would  probably  have  been  used  for  a  contin- 
nous  filter  of  this  size.  The  water-tight  bottom  also  was  dis- 
pensed with,  and  the  gravel  was  prevented  from  sinking  into  the 
silt  by  thin  intermediate  layers  of  graded  materials.  The  saving 
in  cost  was  considerable ;  but,  on  the  other  hand,  a  considerable 
quantity  of  ground-water  comes  up  through  the  bottom  and  in- 
creases the  hardness  of  the  water  from  1.5  to  2.6  parts  of  calcium 
carbonate  in  100,000;  and  while  the  water  when  compared  with 
many  other  waters  is  still  extremely  soft,  the  addition  cannot  be 
regarded  as  desirable.  The  ground-water  also  contains  iron, 
which  increases  the  color  of  the  water  above  what  it  would 
otherwise  be. 

The  underdrains  have  a  frictional  resistance  ten  times  as 
great  as  would  be  desirable  for  a  continuous  filter,  the  idea 
being  to  check  extreme  rates  of  filtration  in  case  of  unequal 
flooding,  and  also  to  limit  the  quantity  of  water  which  could  be 
gotten  through  the  filter  to  that  corresponding  to  a  moderate 
rate  of  filtration. 

The  sand,  instead  of  being  all  of  the  same-sized  grain,  is  of 
two  grades,  with  effective  sizes  respectively  0.25  and  0.30  mm., 
the  coarser  sand  being  placed  farthest  away  from  the  under- 
drains, where  its  greater  distance  is  intended  to  balance  its 
reduced  frictional  resistance  and  make  all  parts  filter  at  an 
equal  rate. 

The  surface  instead  of  being  level  is  waved,  that  is,  there  are 
ridges  thirty  feet  apart,  sloping  evenly  to  the  valleys  one  foot 
deep  half  way  between  them,  to  allow  water  to  be  brought  on 


IN  TERM  I TTEN  T  FIL  7  '-AA  Ttoti.  '•'  ;  O I 

rapidly  without  disturbing  the  sand  surface.  For  the  same 
reason,  as  well  as  to  secure  equality  of  distribution,  a  system  of 
concrete  carriers  for  the  raw  water  goes  to  all  parts  of  the  filter, 
reducing  the  effective  filtering  area  by  4  or  5  per  cent.  The 
filter  is  scraped  as  necessary  in  sections,  the  work  being  per- 
formed when  the  filter  is  having  its  daily  rest  and  aeration. 
Owing  to  the  difference  in  frictional  resistance  before  and  after 
scraping,  and  to  the  fact  that  it  is  impossible  to  scrape  the  entire 
area  in  one  day,  considerable  variations  in  the  rate  of  filtration 
in  different  parts  of  the  filter  must  occur.  The  heavy  frictional 
resistance  of  the  underdrains  when  more  than  the  proper 
quantity  of  water  passes  them  tends  to  correct  this  tendency 
especially  for  the  more  remote  parts  of  the  filter,  but  perhaps 
at  the  expense  of  those  near  to  the  main  drain. 

The  filter  is  not  covered  as  the  suggestions  in  Chapter  II 
would  require,  but  this  is  hardly  on  account  of  its  being  an  in- 
termittent filter. 

The  annual  report  of  the  Massachusetts  State  Board  of 
Health  for  1893  states  that  during  the  first  half  of  December, 
1893,  the  surface  remained  covered,  that  is,  it  was  used  continu- 
ously, and  after  December  i6th  it  was  so  used  when  the  temper- 
ature was  below  24°,  and  was  drained  only  when  the  tempera- 
ture was  24°  or  above.  The  days  on  which  the  filter  was  drained 
during  the  remainder  of  December  are  not  given,  but  during 
January  and  February,  1894,  the  filter  remained  covered  29  days 
and  was  drained  30  days.  Bacterial  samples  were  taken  on  44 
of  these  days,  22  days  when  it  was  drained  and  22  when  it  was 
not.  The  average  number  of  bacteria  on  the  days  when  it  was 
not  drained  was  137  and  on  those  days  when  it  was  drained  252 
per  cubic  centimeter. 

From  February  24th  to  March  I2th  the  number  of  bacteria 
were  unusually  high,  averaging  492  per  cubic  centimeter,  or  5.28 
per  cent  of  the  9308  applied.  During  this  period  the  filter  was 
used  intermittently ;  there  was  ice  upon  it,  and  parts  of  the  sur- 


102.  FILTRATION   OF  PUBLIC  WATER-SUPPLIES. 

face  were  scraped  under  the  ice,  and  high  rates  of  filtration 
undoubtedly  resulted  on  the  scraped  areas.  After  March  I2th 
the  ice  had  disappeared  and  very  much  better  results  were  ob- 
tained. 

While  there  may  be  some  question  as  to  the  direct  cause  of 
this  decreased  efficiency  with  continued  cold  weather  and  ice, 
the  results  certainly  are  not  such  as  to  show  the  advisability  of 
building  open  filters  in  the  Lawrence  climate. 

The  cost  of  building  the  filter  in  comparison  with  European 
niters  was  extraordinarily  low — only  $67,000,  or  $27,000  per  acre 
•of  filter  surface.  To  have  constructed  open  continuous  filters 
of  the  same  area  with  water-tight  bottoms,  divided  into  sections 
with  separate  drains  and  regulating  apparatus,  with  the  necessary 
piping,  would  have  cost  at  least  half  as  much  more,  and  with  the 
masonry  cover  which  I  regard  as  most  desirable  in  the  Lawrence 
climate  the  cost  would  have  been  two  or  three  times  the  ex- 
penditure actually  required. 

It  was  no  easy  matter  to  secure  the  consent  of  the  city  gov- 
ernment to  the  expenditure  of  even  the  sum  used  ;  there  was 
much  skepticism  as  to  the  process  of  filtration  in  general,  and  it 
was  said  that  mechanical  filters  could  be  put  in  for  about  the 
same  cost.  Insisting  upon  the  more  complete  and  expensive 
form  might  have  resulted  either  in  an  indefinite  postponement  of 
action,  or  in  the  adoption  of  an  inferior  and  entirely  inadequate 
process.  Still  I  feel  strongly  that  in  the  end  the  greater  ex- 
pense would  have  proved  an  excellent  investment  in  securing 
softer  water  and  in  the  greater  facility  and  security  of  operating 
the  filter  in  winter. 

In  regard  to  the  effect  of  the  Lawrence  filter  upon  the  health 
of  the  city,  I  can  best  quote  from  Mr.  Mills'  paper  in  the  Report 
of  the  Massachusetts  State  Board  of  Health  for  1893,  and  also 
published  in  the  Journal  of  the  New  England  Water-works 
Association.  Mr.  Mills  says :  "  In  the  following  diagram  [Fig. 
15]  the  average  number  of  deaths  from  typhoid  fever  at  Law- 


IN  TERM  I T  TEN  T  FIL  TRA  TION. 


103 


rence  for  each  month  from  October  to  May,  in  the  preced- 
ing five  years,  are  given  by  the  heavy  dotted  line;  and  the 
number  during  the  past  eight  months  are  given  by  the  heavy 
full  line. 

"The  total  number  for  eight  months  in  past  years  has  been 
forty-three,  and  in  the  present  year  seventeen,  making  a  saving 
of  twenty-six.  Of  the  seventeen  who  died  nine  were  operatives 


y 


-7 


Deaths 


Number  who  used 


no  Canal  Water 


Oct.       Nov.          Dec.        Jan.         Feb.        Mar,         Apr,       May 

FIG.  15. — TYPHOID  FEVER  IN  LAWRENCE. 

in  the  mills,  each  of  whom  was  known  to  have  drunk  unfiltered 
canal  water,  which  is  used  in  the  factories  at  the  sinks  for 
washing. 

"  The  finer  full  line  shows  the  number  of  those  who  died 
month  after  month  who  are  not  known  to  have  used  the 
poisoned  canal  water.  The  whole  number  in  the  eight  months 
is  eight. 

"  It  is  evident  from  the  previous  diagram  [not  reproduced] 
that  the  numbers  above  the  fine  full  line,  here,  follow  after  those 
at  Lowell  in  the  usual  time,  and  were  undoubtedly  caused  by  the 
sickness  at  Lowell ;  but  we  have  satisfactory  reason  to  conclude 
that  the  disease  was  not  propagated  through  the  filter  but  that 
the  germs  were  conveyed  directly  into  the  canals  and  to  those 
who  drank  of  the  unfiltered  canal  water.  Among  the  operatives 


104 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


of  one  of  the  large  corporations  not  using  the  canal  water  there 
was  not  a  case  of  typhoid  fever  during  this  period.  Warnings 
have  been  placed  in  the  mills  where  canal  water  is  used  to 
prevent  the  operatives  from  drinking  it. 

"We  find,  then,  that  the  mortality  from  typhoid  fever  has, 
during  the  use  of  the  filter,  been  reduced  to  40  per  cent  of  the 
former  mortality,  and  that  the  cases  forming  nearly  one  half  of 
this  40  per  cent  were  undoubtedly  due  to  the  continued  use  of 
unfiltered  river  water  drawn  from  the  canals." 

The  records  of  typhoid  fever  in  Lawrence  before  and  after  the 
introduction  of  filters  are  as  follows: 

DEATHS  FROM  TYPHOID  FEVER  IN  LAWRENCE,  1888-98. 


Years. 

Total  Number 
of  Deaths. 

Deaths  per  10,000 
of  Population. 

Persons  who  are  known  to  have  been 
exposed  to  infection. 

By  drinking  Canal 
Water. 

While  living  out 
of  town  just  before 
falling  sick  in 
Lawrence. 

1888 

48 

55 
60 

55 
50 

39 
24 
16 
10 

9 

8 

11.36 
12.66 

13-44 
II.Q4 
10-52 
7.96 
4-75 
3-07 
1.86 
1.62 
i-39 

12 

9 
2 

I 

2 
4 

1889     

1890     

iggi  

1892  

iSoj. 

j8oc 

1896 

1807 

1808          

Filter  put  in  operation  September,  1893. 

Average  rate  before  the  introduction  of  filtered  water  (1888-92). ...    n  .31 
Average  rate  afterward  (1894-98) 2.  54 

These  results  show  a  striking  reduction  in  the  deaths  from 
typhoid  fever  with  the  introduction  of  filtered  water,  which  has 
been  most  gratifying  in  every  way. 

The  more  recent  history  of  the  underdrains  of  the  Lawrence 
filter  is  particularly  instructive.  Owing  to  the  absence  of  a  water- 
tight bottom  to  the  filter,  and  its  low  position,  a  certain  amount 
of  water  constantly  entered  the  filter  from  the  ground  below. 


INTERMITTENT  FIL  TRA  TtON. 


105 


This  water  contained  iron  in  solution  as  ferrous  carbonate.  When 
this  water  came  in  contact  with  the  filtered  water  in  the  gravel  and 
underdrains,  the  iron  was  oxidized  by  the  dissolved  oxygen  carried 
in  the  filtered  water  and  precipitated.  This  was  accompanied  by 
a  growth  of  crenothrix  in  the  gravel  and  underdrains,  which 
gradually  reduced  their  carrying  capacity.  This  reduction  in 


§  a  1  ? 

Dea/6s  aar/0,000  J/'vjno. 

S 

. 

%       % 

^ 

% 

'////////£ 

\JO.O 

1 

I 

'///////// 

** 

'/ 

| 

^ 

-"•<  x".':' 

§^ 

§^ 

/////y///b 

N 

0 

1 

if 

™ 

'/••//s/// 

/y 

^*, 

Wafi 

r  nor  f/. 

terect 

^^ 

Wafer 

f/fterei 

1888       /ffffd      /89O      1891      /39a      S3  93      S3  94     J895      S3  96      /897     /898 

FIG.  16.—  TYPHOID  FEVER  IN  LAWRENCE,  1888  TO  1898. 

carrying  capacity  first  became  apparent  in  cold  weather  when  the 
yield  from  the  filter  was  less  free  than  formerly.  There  was  diffi- 
culty in  maintaining  the  supply  during  the  winter  of  1896-7  and 
more  difficulty  in  the  following  winter. 

The  sand  of  the  filter  was  as  capable  of  filtering  the  full  supply 
of  water  as  it  ever  had  been,  and  the  efficiency  was  as  good ;  but 
the  underdrains  were  no  longer  able  to  collect  the  filtered  water 
and  deliver  it.  As  the  filtering  area  was  ample  for  the  supply, 
it  was  desired  to  avoid  construction  of  additional  filtering  area. 
The  underdrains  were  dug  up  and  cleaned  during  the  periods  when 
the  filter  was  drained.  As  the  filter  is  all  in  one  bed,  the  times 
when  the  filter  could  be  allowed  to  remain  drained,  and  when 
the  work  could  proceed,  were  limited.  Great  care  was  taken  to 
leave  the  work  in  good  condition,  and  free  from  passages,  at  the 
end  of  each  dav's  work,  but  the  numbers  of  bacteria  in  the 


io6 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


effluent  nevertheless  increased  somewhat.  Some  weeks  afterward 
the  number  of  cases  of  typhoid  fever  in  the  city  increased.  The 
numbers  did  not  become  as  high  as  they  had  been  prior  to  the 
introduction  of  filtered  water,  but  they  were  much  higher  than 
they  had  been  since  that  time,  and  they  pointed  strongly  to  the 
disturbance  of  the  underdrains  as  the  cause  of  the  increase. 

The  numbers  of  bacteria  in  the  applied  water  and  in  the 
effluent  from  the  Lawrence  filter  by  months,  from  the  time  the 
filter  was  put  in  operation,  compiled  from  the  reports  of  the  State 
Board  of  Health,  as  far  as  available,  are  as  follows: 

BACTERIA    IN    WATER   APPLIED    TO   AND    EFFLUENT   FROM 

LAWRENCE    FILTER. 

RAW    WATER. 


1893. 

1894. 

1895. 

1896. 

1897. 

1898. 

January   

77OO 

1  8  7OO 

7    COO 

TO   -IT/I 

February  

7  600 

I  C,   O<1O 

12  6oO 

TO      TT°, 

March  

6  500 

2O  77O 

C     QOO 

12  O^  ^ 

37.18 

1  1  200 

8  420 

q  800 

6  QO4 

May  

6  ooo 

7  OOO 

9  6OO 

462^ 

2  O5O 

8  °.oo 

July.. 

2  4.OO 

IO  OOO 

°i  QOO 

6  240 

u>  //b 

2  840 

August         •  . 

3  ioo 

5  ooo 

2  7OO 

8    £7C. 

September             .... 

£7  coo 

6  500 

5  ooo 

12  3OO 

OO/D 

October  

22  2OO 

2C   O-OO 

IQ  OOO 

c   qoo 

November  

10  800 

1  6  600 

8  700 

5  600 

6  6/1/1 

40  TQ 

8   IOO 

SC.ST 

iuy:> 

.301 

Average  ....  .... 

24  6^O 

IO  417 

II    III 

7  108 

10  360 

4gCQ 

EFFLUENT. 


February  

.i^y 
2/1/1 

287 

•i  T  e. 

VA 

7O 

jy 

4^ 

March           •  •  •        .  •  • 

jee 

4O  e 

I  ^7 

67 

0/1 

28l 

84 

4O 

47 

21 

May  

I  "34. 

68 

«;6 

oe 

48 

Tune      ... 

I  IO 

68 

22 

cA 

co 

July  

2C 

CQ 

•2Q 

1  06 

22 

ofi 

aR 

146 

70 

28 

6  850 

42 

4O 

07 

08 

67 

October   .  .                . 

116 

6O 

28 

November   

161 

I7C. 

64 

JU 

07 

66 

December   

in 

0.6/1 

84 

67 

*  I 
24 

^4 

Average   

2  084 

176 

121 

or 

61 

46 

Average  efficiency 

91-55 

98.31 

98.91 

V1 

98.72 

99.41 

4U 
93.95 

INTERMITTENT  FILTRATION.  IO7 

CHEMNITZ  WATER-WORKS. 

The  only  other  place  which  I  have  found  where  anything 
approaching  intermittent  filtration  of  water  is  systematically 
employed  is  Chemnitz,  Germany.  The  method  there  used  bears 
the  same  relation  to  intermittent  filtration  as  does  broad  irriga- 
tion of  sewage  to  the  corresponding  method  of  sewage  treatment; 
that  is,  the  principles  involved  are  mainly  the  same,  but  a  much 
larger  filtering  area  is  used,  and  the  processes  take  place  at  a 
lower  rate  and  under  less  close  control. 

The  water-works  were  built  about  twenty  years  ago  by  plac- 
ing thirty-nine  wells  along  the  Zwonitz  River,  connected  by 
siphon  pipes,  with  a  pumping-station  which  forced  the  water  to 
an  elevated  reservoir  near  the  city  (Fig.  17).  The  wells  are  built 


ii  men  tation 

J..        gffg.     T  .  _- -V-  JV,,       - 

^"V 

.River 

100         200        300        400        600        600        TOO        800        WOMeten 

600  1000  1500  2000  8500  3000  Feet 

FIG.  17. — PLAN  OF  AREA  USED  FOR  INTERMITTENT  FILTRATION  AT  CHEMNITZ. 

of  masonry,  5  or  6  feet  in  diameter  and  10  or  12  feet  deep,  and 
are  on  the  rather  low  bank  of  the  river.  The  material,  with  the 
exception  of  the  surface  soil,  and  loam  about  3  feet  deep,  is  a 
somewhat  mixed  gravel  with  an  effective  size  of  probably  from 
0.25  to  0.50  mm.,  so  that  water  is  able  to  pass  through  it  freely. 
The  wells  are,  on  an  average,  about  120  feet  apart,  and  the  line 
is  seven  eighths  of  a  mile  long. 

It  was  found  that  in  dry  times  the  ground-water  level  in  the 


108  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

entire  neighborhood  was  lowered  some  feet  below  the  level  of 
the  river  without  either  furnishing  water  enough  or  stopping 
the  flow  of  the  river  below.  The  channel  of  the  river  was  so 
silted  that,  notwithstanding  the  porous  material,  the  water  could 
not  penetrate  it  to  go  toward  the  wells. 

A  dam  was  now  built  across  the  river  near  the  pumping- 
station,  and  a  canal  was  dug  from  above  the  dam,  crossing  the 
line  of  wells  and  running  parallel  to  it  on  the  back  side  for  about 
half  a  mile.  Later  a  similar  canal  was  dug  back  of  the  remain- 
ing upper  wells.  Owing  to  the  difference  in  level  in  the  river 
above  and  below,  the  canals  can  be  emptied  and  filled  at 
pleasure.  They  are  built  with  carefully  prepared  sand  bottoms, 
and  the  sand  sides  are  protected  by  an  open  paving,  to  allow  the 
percolation  of  as  much  water  as  possible,  and  the  sand  is  cleaned 
by  scraping,  as  is  usual  with  ordinary  sand  filters,  once  a  year  or 
oftener. 

The  yield  from  the  wells  was  much  increased  by  these  canals, 
but  the  water  of  the  river  is  polluted  to  an  extent  which  would 
ordinarily  quite  prevent  even  the  thought  of  its  being  used  for 
water-supply,  and  it  was  found  that  the  water  going  into  the 
ground  from  the  canals,  and  passing  through  the  always  satu- 
rated gravel  to  the  wells,  without  coming  in  contact  with  air  at 
any  point,  after  a  time  contained  iron  and  had  an  objectionable 
odor. 

To  avoid  this  disagreeable  result  the  meadow  below  the 
pumping-station  was  laid  out  as  an  irrigation  field  (Fig.  16). 
The  water  from  above  the  dam  was  taken  by  a  canal  on  the 
opposite  side  of  the  river  through  a  sedimentation  pond  (which, 
however,  is  not  now  believed  to  be  necessary  and  is  not  always 
used),  and  then  under  the  river  by  a  siphon  to  a  slightly  ele- 
vated point  on  the  meadow,  from  which  it  is  distributed  by 
a  system  of  open  ditches,  exactly  as  in  sewage  irrigation.  The 
area  irrigated  is  not  exactly  defined  and  varies  somewhat  from 
time  to  time;  the  rate  of  filtration  may  be  roughly  estimated 


INTERMITTENT  FILTRATION.  ICX) 

at  from  100,000  to  150,000  gallons  per  acre  daily,  although 
limited  portions  may  occasionally  get  five  times  these  quantities 
for  a  single  day.  The  water  passes  through  the  three  feet  of 
soil  and  loam,  and  afterward  through  an  average  of  six  feet 
of  drained  coarse  sand  or  gravel  in  which  it  meets  air,  and 
afterward  filters  laterally  through  the  saturated  gravel  to  the 
wells.  The  water  so  obtained  is  invariably  of  good  quality  in 
every  way,  colorless,  free  from  odor  and  from  bacteria.  The 
surface  of  the  irrigated  land  is  covered  with  grass  and  has  fruit- 
trees  (mostly  apple)  at  intervals  over  its  entire  area. 

This  first  system  of  irrigation  is  entirely  by  gravity.  On 
account  of  natural  limits  to  the  land  it  could  not  be  conveniently 
extended  at  this  point,  and  to  secure  more  area,  the  higher  land 
above  the  pumping-station  was  being  made  into  an  irrigation 
field  in  1894.  This  is  too  high  to  be  flooded  by  gravity,  and  will 
be  used  only  for  short  periods  in  extremely  dry  weather.  The 
water  is  elevated  the  few  feet  necessary  by  a  gas-engine  on  the 
river-bank.  In  times  of  wet  weather  enough  water  is  obtained 
from  the  wells  without  irrigation,  and  the  land  is  only  irrigated 
when  the  ground-water  level  is  too  low. 

During  December,  January,  and  February  irrigation  is 
usually  impossible  on  account  of  temperature,  and  the  canals  are 
then  used,  keeping  them  filled  with  water  so  that  freezing  to  the 
bottom  is  impossible ;  but  trouble  with  bad  odors  in  the  filtered 
water  drawn  from  the  wells  is  experienced  at  these  times. 

The  drainage  area  of  the  Zwonitz  River  is  only  about  44 
square  miles,  and  upon  it  are  a  large  number  of  villages  and 
factories,  so  that  the  water  is  excessively  polluted.  The  water 
in  the  wells,  however,  whether  coming  from  natural  sources,  or 
from  irrigation,  or  from  the  canals,  has  never  had  as  many  as  100 
bacteria  per  cubic  centimeter,  and  is  regarded  as  entirely 
wholesome. 

In  extremely  dry  weather  the  river,  even  when  it  is  all  used 
for  irrigation  so  that  hardly  any  flows  away  below,  cannot  be 


IIO  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

made  to  supply  the  necessary  daily  quantity  of  2,650,000  gal- 
lons, and  to  supply  the  deficiency  at  such  times,  as  well  as  to 
avoid  the  use  of  the  canals  in  winter,  a  storage  reservoir  hold- 
ing 95,000,000  gallons  has  recently  been  built  on  a  feeder  of  the 
river.  This  water,which  is  from  an  uninhabited  drainage  area, 
is  filtered  through  ordinary  continuous  filters  and  flows  to  the 
city  by  gravity.  Owing  to  the  small  area  of  the  watershed  it  is 
incapable  of  supplying  more  than  a  fraction  of  the  water  for  the 
city,  and  will  be  used  to  supplement  the  older  works. 

This  Chemnitz  plant  is  of  especial  interest  as  showing  the 
successful  utilization  of  a  river-water  so  grossly  polluted  as 'to 
be  incapable  of  treatment  by  the  ordinary  methods.  Results 
obtained  at  the  Lawrence  Experiment  Station  have  shown  that 
sewage  is  incapable  of  being  purified  by  continuous  filtration, 
the  action  of  air  being  essential  for  a  satisfactory  result.  With 
ordinary  waters  only  moderately  polluted  this  is  not  so  ;  for 
they  carry  enough  dissolved  air  to  effect  their  own  purifica- 
tion. In  Chemnitz,  however,  as  shown  by  the  results  with  the 
canals,  the  pollution  is  so  great  that  continuous  filtration  is 
inadequate  to  purify  the  water,  and  the  intermittent  filtration 
adopted  is  the  only  method  likely  to  yield  satisfactory  results  in 
such  cases. 

Intermittent  filtration  is  now  being  adopted  for  purifying 
orooks  draining  certain  villages  and  discharging  into  the  ponds 
or  reservoirs  from  which  Boston  draws  its  water-supply.  The 
water  of  Pegan  Brook  below  Natick  has  been  so  filtered  since 
1893  with  most  satisfactory  results,  and  affords  almost  absolute 
protection  to  Boston  from  any  infection  which  might  otherwise 
enter  the  water  from  that  town.  A  similar  treatment  is  soon  to 
be  given  to  a  brook  draining  the  city  of  Marlborough.  The 
sewage  from  these  places  is  not  discharged  into  the  brooks,  but 
is  otherwise  provided  for,  but  nevertheless  they  receive  many 
polluting  matters  from  the  houses  and  streets  upon  their  banks. 

The  filtration  used  resembles  in  a  measure  that  at  Chemnitz. 


INTERMITTENT  FILTRATION,  III 

and  1  am  informed  by  the  engineer,  Mr.  Desmond  FitzGerald, 
that  it  was  adopted  on  account  of  its  convenience  for  this  partic- 
ular problem,  and  not  because  he  attaches  any  special  virtue  to. 
the  intermittent  feature. 

APPLICATION  OF  INTERMITTENT  FILTRATION. 

In  regard  to  the  use  of  waters  as  grossly  polluted  as  the 
Zwonitz,  the  tendency  is  strongly  to  avoid  their  use,  no  matter 
how  complete  the  process  of  purification  may  be;  but  in  case  it 
should  be  deemed  necessary  to  use  so  impure  a  water  fora  public 
supply,  intermittent  filtration  is  the  only  process  known  which 
would  adequately  purify  it.  And  it  should  be  used  at  compara- 
tively low  rates  of  nitration.  I  believe  that  an  attempt  to  filter 
the  Zwonitz  at  the  rate  used  for  the  Merrimac  water  at  Law- 
rence, which  is  by  comparison  but  slightly  polluted,  would  re- 
sult disastrously. 

The  operation  in  winter  must  also  be  considered.  Intermit- 
tent filtration  of  sewage  on  open  fields  in  Massachusetts  winters 
is  only  possible  because  of  the  comparatively  high  temperature 
of  the  sewage  (usually  40°  to  50°),  and  would  be  a  dismal  failure 
with  sewage  at  the  freezing-point,  the  temperature  to  be  ex- 
pected in  river-waters  in  winter. 

It  is  impossible  to  draw  a  sharp  line  between  those  waters 
which  are  so  badly  polluted  as  to  require  intermittent  filtration 
for  their  treatment  and  those  which  are  susceptible  to  the  ordi- 
nary continuous  filtration.  Examples  of  river-waters  polluted 
probably  beyond  the  limits  reached  in  any  American  waters 
used  for  drinking  purposes  and  successfully  filtered  with  contin- 
uous filters  are  furnished  by  Altona,  Breslau,  and  London. 

Intermittent  filtration  may  be  considered  in  those  cases 
where  it  is  proposed  to  use  a  water  polluted  entirely  beyond  the 
ordinary  limits,  and  for  waters  containing  large  quantities  of  de- 
composable organic  matters  and  microscopical  organisms;  but  in 
those  cases  where  a  certain  and  expeditious  removal  of  mud  is 


112  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

desired,  and  where  waters  are  only  moderately  polluted  by 
sewage,  but  still  in  their  raw  state  are  unhealthy,  it  is  not  ap- 
parent that  intermittent  filtration  has  any  advantages  commen- 
surate with  the  disadvantages  of  increased  rate  to  produce  the 
same  total  yield  and  of  the  increased  difficulty  of  operation, 
particularly  in  winter;  and  in  such  cases  continuous  filtration  is 
to  be  preferred. 

In  the  removal  of  tastes  and  odors  from  pond  or  reservoir 
waters  which  are  not  muddy,  but  which  are  subject  to  the  growths 
of  low  forms  of  plants,  which  either  by  their  growth  or  decomposi- 
tion impart  to  the  water  disagreeable  tastes  and  odors,  intermittent 
filtration  may  have  a  distinct  advantage.  In  such  cases  there  is 
often  an  excess  of  organic  matter  to  be  disposed  of  by  oxidation, 
and  the  additional  aeration  secured  by  intermittent  filtration  is  of 
substantial  assistance  in  disposing  of  these  matters. 


TURBIDITY  AND    COLOR.  113 


CHAPTER   VIII. 

TURBIDITY    AND    COLOR,   AND    THE   EFFECT   OF    MUD    UPON 

SAND-FILTERS. 

THE  ideal  water  in  appearance  is  distilled  water,  which  is  per- 
fectly clear  and  limpid,  and  has  a  slight  blue  color.  When  other 
waters  are  compared  with  it,  the  divergences  in  color  from  the 
color  of  distilled  water  are  measured,  and  not  the  absolute  colors 
of  the  waters.  Many  spring  waters  and  filtered  waters  are  indis- 
tinguishable in  appearance  from  distilled  water. 

Public  water-supplies  from  surface  sources  contain  two  sub- 
stances or  classes  of  substances  which  injure  their  appearance, 
namely,  peaty  coloring  matters,  and  mud.  Waters  discolored  by 
peaty  matters  are  most  common  in  New  England  and  in  certain 
parts  of  the  Northwest,  while  muddy  waters  are  found  almost 
everywhere,  but  of  different  degrees  of  muddiness,  according  to 
the  physical  conditions  of  the  water-sheds  from  which  they  are 
obtained. 

Muddy  waters  are  often  spoken  of  as  colored  waters,  and  in  a 
sense  this  is  correct  where  the  mud  consists  of  clays  or  other 
materials  having  distinct  colors;  but  it  is  more  convenient  to 
classify  impurities  of  this  kind  as  turbidities  only,  and  to  limit  the 
term  colored  waters  to  those  waters  containing  in  solution  vege- 
table matters  which  color  them. 

The  removal  of  either  color  or  turbidity  may  be  called  clarifi- 
cation. 

Colored  waters  are  usually  drawn  from  water-sheds  where  the 
underlying  rock  is  hard  and  does  not  rapidly  disintegrate,  and 
where  the  soils  are  firm  and  sandy,  and  especially  from  swamps. 
The  water  here  comes  in  contact  with  peat  or  muck,  which  colors 


114  FILTRATIO.V    OF  PUBLIC    WATER-SUPPLIES. 

it,  but  is  so  firm  as  not  to  be  washed  by  flood  flows,  and  so  does 
not  cause  turbidity. 

Large  parts  of  the  United  States  have  for  rock  foundations 
shales  or  other  soft  materials  which  readily  disintegrate  when 
exposed,  and  which  form  clayey  soils  readily  washed  by  hard  rains. 
Waters  from  such  watersheds  are  generally  turbid  and  very  rarely 
colored.  In  fact  a  water  carrying  much  clay  in  suspension  is 
usually  found  colorless  when  the  clay  is  removed,  even  if  it  were 
originally  colored.  It  thus  happens  that  waters  which  are  colored 
and  turbid  at  the  same  time  hardly  exist  in  nature. 

Color-producing  matters  and  turbidity-producing  matters  are 
different  in  their  natures,  and  the  methods  which  must  be  used 
to  remove  them  are  different. 


THE    MEASUREMENT    OF    COLOR. 

The  colors  of  waters  are  measured  and  recorded  by  comparing 
them  with  colors  of  solutions  or  substances  which  are  permanent, 
or  which  can  be  reproduced  at  will.  One  of  the  earliest  methods 
of  measuring  colors  of  waters  was  to  compare  them  with  the 
colors  of  the  Nessler  standards  used  for  the  estimation  of  ammonia 
in  water  analysis.  The  Nessler  standards  were  similar  in  appear- 
ance to  yellow  waters,  and  their  colors  depended  upon  the  amounts 
of  ammonia  which  had  been  used  in  preparing  them,  and  a  record 
was  made  of  the  standard  which  most  closely  resembled  the  water 
under  examination. 

The  method  was  open  to  the  serious  objections  that  the  hues 
of  the  standards  did  not  match  closely  the  hues  of  the  waters;  that 
the  colors  produced  with  different  lots  of  Nessler  reagent  differed 
considerably,  and  therefore  the  exact  values  of  results  were  more 
or  less  uncertain ;  and  further,  that  the  numbers  obtained  for 
color  were  not  even  approximately  proportional  to  the  amounts  of 
coloring  matter  present.  Because  of  this  peculiarity,  in  filtration 
the  percentage  of  color  removal,  as  determined  by  the  use  of  these 


TURBIDITY  AND    COLOR.  11$ 

standards,  is  not  even  approximately  correct,  but  is  much  above 
the  truth. 

In  the  Lovibond  tintometer,  which  has  been  extensively  used 
in  England,  the  rtandards  of  color  are  based  upon  the  colors  of 
certain  glass  slips,  which  are  in  turn  compared  with  standard 
originals  kept  for  that  purpose.  This  process  answers  quite  well, 
but  is  open  to  some  objections  because  of  possible  uncertainties 
in  the  standardization  of  the  units. 

Another  method  of  measuring  colors  is  to  compare  them  with 
dilute  solutions  of  platinum  and  cobalt.  The  ratio  of  cobalt  to 
platinum  can  be  varied  to  make  the  hue  correspond  very  closely 
with  the  hues  of  natural  waters,  and  the  amount  of  platinum 
required  to  match  a  water  affords  a  measure  of  its  color,  one  part 
of  metallic  platinum  in  10,000  parts  of  water  forming  the  unit  of 
color. 

This  standard  has  the  advantages  that  it  can  be  readily  pre- 
pared with  absolute  accuracy  in  any  laboratory,  and  that  by  vary- 
ing the  ratio  of  platinum  to  cobalt  the  hues  of  various  waters  can 
be  most  perfectly  matched.  It  is  important  that  the  observations 
should  not  be  made  in  too  great  a  depth,  as  the  discrepancy  in 
hues  increases  much  more  rapidly  than  the  depth  of  color. 

For  further  information  regarding  colors  the  reader  is  referred 
to  articles  in  the  American  Chemical  Journal,  1892,  vol.  xiv, 
page  300;  Journal  of  the  American  Chemical  Society,  vol.  ii, 
page  8;  vol.  xviii,  1896,  pp.  68,  264,  and  484;  Journal  of  the 
Franklin  Institute,  Dec.  1894,  p.  402;  Journal  of  the  New 
England  Water  Works  Association,  vol.  xiii,  1898,  p.  94. 


AMOUNT   OF   COLOR   IN   AMERICAN   WATERS. 

New  England  surface-waters  have  colors  ranging  from  almost 
nothing  up  to  2.00.  The  colors  of  the  public  water-supplies •  of 
Massachusetts  cities  have  been  recorded  in  the  reports  of  the  State 
Board  of  Health  for  some  ten  years.  The  figures  given  were 


116 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


1857  /888  J889  J8SO 


1.0 


New  Bed  ford 

FIG.  18. — COLORS  OF  WATERS. 

(Analyses  of  the  Mass.  State  Board  of  Health.) 


TURBIDITY  AND    COLOR.  1 1/ 

recorded  first  upon  the  Nessler  standard,  and  afterwards  upon  a 
modification  of  the  same,  known  as  the  natural  water  standard. 
The  figures  given  are  approximately  equal  to  those  for  the  plati- 
num color  standard,  the  relations  between  the  two  having  been 
frequently  determined  by  various  observers  and  published  in  the 
above-mentioned  papers.  The  accompanying  diagram  shows  the 
colors  in  several  Massachusetts  supplies,  as  plotted  from  the 
figures  given  in  the  published  reports. 

In  Connecticut  also  the  colors  of  many  public  water-supplies 
have  been  recorded  in  the  reports  of  the  State  Board  of  Health 
on  the  platinum  color-standard. 

The  waters  of  the  Middle  States,  with  rare  exceptions,  are 
almost  free  from  color.  In  the  Northwest  waters  are  obtained 
often  with  very  high  colors,  even  considerably  higher  than  the 
New  England  waters,  and  some  of  the  Southern  swamps  also  yield 
highly  colored  waters. 

REMOVAL    OF    COLOR. 

Peaty  coloring-matter  is  almost  perfectly  in  solution,  and  only 
a  portion  of  it  is  capable  of  being  removed  by  any  form  of  simple 
filtration.  In  order  to  remove  the  coloring-matter  it  is  necessary 
to  change  it  chemically,  or  to  bring  it  into  contact  with  some  sub- 
stance capable  of  absorbing  it.  For  this  reason  sand  filtration 
with  ordinary  sands,  having  no  absorptive  power  for  color,  com- 
monly removes  only  from  one  fourth  to  one  third  of  the  color  of 
the  raw  water. 

MEASUREMENT   OF   TURBIDITY. 

The  amount  of  mud  or  turbidity  in  a  water  is  often  expressed 
as  the  weight  of  the  suspended  matters  in  a  given  weight  of  the 
water.  Most  of  the  data  relating  to  turbidities  of  waters  are 
stated  in  this  way,  because  this  was  the  only  method  recognized 
by  the  earlier  investigators. 


Il8  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

This  method  of  statement  has  some  disadvantages:  it  fails  to 
take  into  account  the  different  sizes  of  particles  which  are  carried 
in  suspension  by  different  waters,  and  at  different  times.  Thus 
the  Merrimac  River  in  a  great  flood  may  carry  100  parts  in 
100,000  of  fine  sand  in  suspension,  and  still  it  could  hardly  be 
called  muddy;  while  another  stream  carrying  only  a  fraction  of 
this  amount  of  fine  clay  would  be  extremely  muddy.  Further,  an 
accurate  determination  of  suspended  matters  is  a  very  troublesome 
and  tedious  operation,  and  cannot  be  undertaken  as  frequently  as 
is  necessary  for  an  adequate  study  of  the  mud  question. 

Turbidity  is  principally  important  as  it  affects  the  appearance 
of  water,  and  it  would  seem  that  optical  rather  than  gravimetric 
methods  should  be  used  for  its  determination.  Various  optical 
methods  of  measuring  turbidity  have  been  proposed.  The  general 
method  employed  is  to  measure  the  thickness  of  the  layer  of 
water  through  which  some  object  can  be  seen  under  definite 
conditions  of  lighting.  The  most  accurate  results  can  probably 
be  obtained  in  closed  receptacles  and  with  artificial  light.  Such  a 
method  has  been  used  by  Mr.  G.  W.  Fuller  at  Louisville  and 
Cincinnati  in  connection  with  his  experiments,  and  is  described 
by  Parmelee  and  Ellms  in  the  Technology  Quarterly  for  June, 
1899.  This  apparatus  is  called  by  Mr.  Fuller  a  diaphanometer. 

At  the  Lawrence  Experiment  Station  of  the  Massachusetts 
State  Board  of  Health  as  early  as  1889  it  became  necessary  to 
express  the  turbidities  of  various  waters  approximately,  and  the 
very  simple  device  of  sticking  a  pin  into  a  stick,  and  pushing  it 
down  into  the  water  under  examination  as  far  as  it  could  be  seen, 
was  adopted.  Afterwards  a  platinum  wire  0.04  of  an  inch  in 
diameter  was  substituted  for  the  pin,  and  the  stick  was  graduated 
so  that  the  turbidities  could  be  read  from  it  directly.  The  figures 
on  the  stick  were  inversely  proportional  to  their  distances  from  the 
wire.  When  the  wire  could  be  seen  one  inch  below  the  surface, 
the  turbidity  was  reported  as  i.oo;  when  the  wire  could  be  seen 
two  inches,  the  turbidity  was  0.50,  and  when  it  could  be  seen  ten 


TURBIDITY  AND    COLOR.  I TQ 

inches  the  turbidity  was  o.  10,  etc.  This  scale  is  much  more  con- 
venient than  a  scale  showing  the  depth  at  which  the  wire  can  be 
seen ;  and  within  certain  limits  the  figures  obtained  with  it  are 
directly  proportional  to  the  amount  of  the  elements  which  obstruct 
light  in  the  water.  Thus,  if  a  water  having  a  turbidity  of  i.oo  is 
mixed  with  an  equal  volume  of  clear  water,  the  mixture  will  have 
a  turbidity  of  0.50.  Advantage  is  taken  of  this  fact  for  the 
measurement  of  turbidities  so  great  that  they  cannot  be  accurately 
determined  by  direct  observation.  For  turbidities  much  above 
i.oo  it  is  very  difficult  to  read  the  depth  of  wire  with  sufficient 
accuracy,  and  such  waters  are  diluted  with  one,  two,  or  more  times 
their  volume  of  clear  water  in  a  pail  or  other  receptacle,  the 
turbidity  of  the  diluted  water  is  taken,  and  multiplied  by  the 
appropriate  factor. 

For  the  greatest  accuracy  it  is  necessary  that  the  observations 
should  be  taken  in  the  open  air  and  not  under  a  roof.  They 
should  preferably  be  made  in  the  middle  of  the  day  when  the  light 
is  strongest,  and  in  case  the  sun  is  shining,  the  wire  must  be  kept 
in  shadow  and  not  in  direct  sunlight. 

The  turbidities  of  effluents  are  usually  so  slight  that  they 
cannot  be  taken  in  this  manner;  in  fact,  turbidities  of  less  than 
0.02,  with  the  wire  visible  50  inches  below  the  surface,  cannot 
be  conveniently  read  in  this  way.  For  the  estimation  of  lower 
turbidities  a  water  is  taken  having  a  turbidity  of  0.03  or  0.04 
and  as  free  as  possible  from  large  suspended  particles.  The  tur- 
bidity of  this  water  is  measured  by  a  platinum  wire  in  the  usual 
way,  and  the  water  is  then  diluted  with  clear  water  to  make 
standards  for  the  lower  turbidities. 

The  comparisons  between  standards  and  waters  are  best  made 
in  bottles  of  perfectly  clear  glass,  holding  at  least  a  gallon,  and 
the  comparison  is  facilitated  by  surrounding  the  bottles  with  black 
cloth  except  at  the  point  of  observation,  and  lighting  the  water 
by  electric  lights  so  arranged  that  the  light  passes  through  the 
water  but  is  hidden  from  the  observer.  In  case  the  water  under 


120  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

examination  is  colored,  the  comparison  is  rendered  difficult,  and 
it  is  often  advisable  to  add  a  small  amount  of  methyl  orange  to 
the  standards  to  make  the  colors  equal. 

Instead  of  diluting  a  water  of  known  turbidity  for  the  standards, 
a  standard  can  be  made  by  precipitating  a  known  amount  of  silver 
chloride  in  the  water.  For  this  purpose  about  one  per  cent  of 
common  salt  is  dissolved  in  clear  water  and  small  measured  amounts 
of  silver  nitrate  added,  until  the  turbidity  produced  is  equal  to  that 
of  the  water  under  examination.  The  relation  of  the  amount  of 
silver  nitrate  used  to  the  turbidity  is  entirely  arbitrary,  and  is 
established  by  comparisons  of  standards  made  in  this  way  with 
waters  having  turbidities  from  0.02  to  0.04,  the  turbidities  of 
which  are  measured  with  the  platinum  wire,  and  which  afterwards 
serve  to  rate  the  standards.  The  silver  chloride  has  a  slight  color, 
which  is  an  objection  to  its  use,  and  perhaps  some  other  substance 
could  be  substituted  for  it  with  advantage.  The  standards  have 
to  be  made  freshly  each  day. 

One  disadvantage  of  the  platinum-wire  method  of  observing 
turbidities  in  the  open  air,  as  compared  with  the  diaphanometric 
method  using  artificial  light,  is  that  observations  cannot  be  made 
in  the  night.  To  get  the  general  character  of  the  water  in  a 
stream,  daily  observations  taken  about  noon  will  generally  be 
sufficient;  but  for  some  purposes  it  is  important  to  know  the 
turbidity  at  different  hours  of  the  day,  and  in  such  cases  the 
platinum-wire  method  is  at  a  distinct  disadvantage.  Variations 
in  the  amount  of  light,  within  reasonable  limits,  do  not  affect  the 
results  materially,  although  extreme  variations  are  to  be  avoided. 
The  size  of  the  wire  also  influences  the  results  somewhat.  The 
wire  commonly  used  is  0.04  of  an  inch  or  one  millimeter  in 
diameter.  A  wire  only  four  tenths  of  this  size  in  some  experi- 
ments at  Pittsburg  gave  results  25  per  cent  higher;  with  a  wire 
twice  as  large  the  results  were  lower,  but  the  differences  were 
much  less.  Wire  0.04  of  an  inch  in  diameter  was  adopted  as 
being  very  well  adapted  to  rather  turbid  river-waters.  For  very 


TURBIDITY  AND    COLOR.  121 

clear  lake  or  reservoir  waters,  usually  transparent  to  a  great  depth, 
a  much  larger  object  is  preferable.  Within  certain  limits  the 
results  obtained  with  an  object  of  any  size  can  be  converted  into 
corresponding  figures  for  another  object,  or  another  light,  by  the 
use  of  a  constant  factor.  Thus  the  turbidities  obtained  with  a 
platinum  wire  always  have  approximately  the  same  ratio  to  the 
turbidities  of  the  same  waters  determined  by  the  diaphanometer. 

The  platinum-wire  method  has  been  used  in  many  cases  with 
most  satisfactory  results.  If  it  lacks  something  in  theoretical 
accuracy  as  compared  with  more  elaborate  methods,  it  more  than 
makes  up  for  it  by  its  simplicity ;  and  reliable  observations  can  be 
taken  with  it  by  people  who  would  be  entirely  incompetent  to 
operate  more  elaborate  apparatus;  and  it  can  thus  be  used  in 
many  cases  where  other  methods  would  be  impossible. 

Upon  this  scale  the  most  turbid  waters  which  have  come  under 
the  observation  of  the  author  have  turbidities  of  about  2.50, 
although  waters  much  more  turbid  than  this  undoubtedly  exist. 
A  water  with  a  turbidity  of  i.oo  is  extremely  muddy,  and  only 
one  tenth  of  this  turbidity  would  cause  remark  and  complaint 
among  those  who  use  it  for  domestic  purposes.  In  an  ordinary 
pressed-glass  tumbler  a  turbidity  of  0.02  is  just  visible  to  an 
ordinary  observer  who  looks  at  the  water  closely,  but  it  is  not 
conspicuous,  nor  would  it  be  likely  to  cause  general  complaint; 
and  this  amount  may  be  taken  as  approximately  the  allowable 
limit  of  turbidity  in  a  good  public  water-supply.  In  a  carefully 
polished,  and  perfectly  transparent  glass  a  turbidity  of  o.oi  will 
be  visible,  and  in  larger  receptacles  still  lower  turbidities  may  be 
seen  if  the  water  is  examined  carefully.  In  gallon  bottles  of  very 
clear  glass,  under  electric  light  and  surrounded  by  black  cloth,  a 
turbidity  of  o.ooi  can  be  distinguished,  but  a  turbidity  even 
several  times  as  large  as  this  could  hardly  be  detected  except'  by 
the  use  of  special  appliances,  or  where  water  is  seen  in  a  depth  of 
several  feet. 


122 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


RELATION    OF    PLATINUM-WIRE   TURBIDITIES    TO    SUSPENDED 

MATTERS. 

The  relation  of  turbidity  to  the  weight  of  suspended  matters  is 
approximately  constant  for  waters  from  which  the  coarser  matters 
have  been  entirely  removed  by  sedimentation.  For  these  waters 
the  suspended  matters  in  parts  per  100,000  are  about  16  times  the 
turbidity.  For  river- waters  the  ratios  are  always  larger.  With 
very  sluggish  rivers  the  ratio  is  only  a  little  larger  than  for  settled 
waters.  For  average  river-waters  the  ratio  is  considerably  higher, 
and  increases  with  the  turbidity,  and  for  very  rapid  rivers  and 
.torrents  the  ratio  is  much  wider,  as  the  suspended  matters  consist 
largely  of  particles  which  are  heavy  but  do  not  increase  very  much 
the  turbidity. 

The  following  table  gives  the  amounts  of  suspended  matters 
for  various  classes  of  waters  corresponding  to  the  turbidities  stated, 
which  have  been  deduced  from  the  experience  of  the  author.  It 
is  very  likely  that  ratios  different  from  the  above  would  be 
obtained  with  waters  in  which  the  sediment  was  of  different 
character. 


Suspended  Matters:   Parts  in  100,000. 

Turbidity, 
Platinum-wire 

Standard. 

Settled  Waters. 

River  Waters, 
Finest  Sediment. 

River  Waters, 
Average  Sediment. 

Rivet  Waters, 
Coarsest  Sediment. 

O.OI 

0.16 

0.05 

0.80 

0.85 

1-30 

2.40 

O.  IO 

i.  60 

i-75 

2.6o 

4.90 

0.20 

3-20 

3-60 

5-50 

10.00 

0.30 

4.80 

5-70 

8.50 

15.00 

0.40 

6.40 

7.80 

1  1.  60 

21.00 

0.50 

8.00 

IO.OO 

15.00 

26.OO 

1.  00 

16.00 

23.00 

36.00 

59-oo 

1-50 

24.00 

40.00 

62.00 

97.00 

2.OO 

32.00 

61.00 

94.00 

140.00 

3-oo 

48.00 

I  IO.OO 

175-00 

250.00 

TURBIDITY  AND    COLOR.  123 


SOURCE   OF   TURBIDITY. 

Much  turbidity  originates  in  plowed  fields  of  clayey  soil,  or  in 
fields  upon  which  crops  are  growing.  If  it  has  not  rained  for 
some  days,  and  the  surface-soil  is  comparatively  dry,  the  first  rain 
that  falls  upon  such  land  is  absorbed  by  the  pores  of  the  soil  until 
they  are  filled.  If  the  rain  is  not  heavy,  but  little  runs  off  over 
the  surface.  If,  however,  the  rain  continues  rapidly  after  the 
surface-soil  is  saturated,  the  excess  runs  off  over  the  surface  to  the 
nearest  watercourse.  The  impact  of  the  rain-drops  upon  the  soil 
loosens  the  particles,  and  the  water  flowing  off  carries  some  of  them 
in  suspension,  and  the  water  is  said  to  be  muddy. 

The  particles  carried  off  in  this  way  are  extremely  small. 
Mr.  George  W.  Fuller,  in  his  report  upon  water  purification  at 
Louisville,  estimates  that  many  of  them  are  not  more  than  a 
hundred  thousandth  of  an  inch  in  diameter,  and  not  more  than  a 
tenth  as  large  as  common  water  bacteria. 

The  turbidity  of  the  water  flowing  from  a  field  of  loose  soil 
may  be  2.00  or  more;  that  is  to  say,  the  wire  is  hidden  by  a 
depth  of  half  an  inch  of  water  or  less.  When  the  water  reaches 
the  nearest  watercourse  it  meets  with  water  from  other  kinds  of 
land,  such  as  woodlands  and  grassed  fields,  and  these  waters  are 
less  turbid.  The  water  in  the  first  little  watercourse  is  thus  a 
mixture  and  has  a  turbidity  of  perhaps  i.oo. 

The  conditions  which  control  the  turbidity  of  any  brook  are 
numerous  and  complicated.  The  turbidity  of  a  stream  receiving 
various  brooks  depends  upon  the  turbidities  of  all  the  waters 
coming  into  it.  Generally  speaking,  the  turbidity  of  a  river 
depends  directly  upon  the  turbidities  of  its  feeders,  and  is  not 
affected  materially  by  erosion  of  its  bed  or  by  sedimentation  in 
it.  There  are,  of  course,  some  streams  which  in  times  of  great 
floods  cut  their  banks,  and  all  streams  pick  up  and  move  about 
from  place  to  place  more  or  less  of  the  sand  and  other  coarse 


I24 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


materials  upon  their  bottoms.     The  materials  thus  moved,  how- 
ever, have  but  little  influence  upon  the  turbidity. 

After  the  rain  is  over  some  of  the  water  held  by  the  soil  will 
find  its  way  to  the  watercourses  by  underground  channels,  and 
will  prevent  the  stream  from  drying  up  between  rains,  but  the 
average  volume  of  the  stream-flows  between  rains  will  be  much 


tec. 


FIG.  19. — FLUCTUATIONS  IN  TURBIDITY  OF  THE  WATER  OF  THE  ALLEGHENY 

RlVER   AT    PlTTSBURG    DURING    1898. 

less  than  the  volumes  during  the  rains  when  the  water  is  most 
turbid. 

These  conditions  are  well  illustrated  by  a  few  data  upon  the 
turbidity  of  three  Pennsylvania  streams,  recently  collected  by  the 
author.  One  of  these  streams  is  a  small  brook  having  a  drainage 
area  of  less  than  three  square  miles.  The  observations  extended 
over  a  period  of  47  days.  During  this  time  there  were  five  floods, 
or  an  average  of  one  flood  in  ten  days.  The  duration  of  floods 
was  less  than  twenty-four  hours  in  each  case.  Selecting  the  days 
when  the  turbidity  was  the  highest,  to  the  number  of  one  tenth 


TURBIDITY  AND    COLOR.  12$ 

•of  the  whole  number  of  days,  the  sum  of  the  turbidities  for  these 
<lays  was  67  per  cent  of  the  aggregate  turbidities  for  the  whole 
period.  That  is  to  say,  67  per  cent  of  the  whole  amount  of  mud 
was  in  the  water  of  only  a  tenth  of  the  days;  the  water  of  the 
other  nine  tenths  of  the  days  contained  only  33  per  cent  of  the 
whole  amount  of  turbidity.  The  average  turbidity  of  the  water 
for  the  flood  days  was  eighteen  times  as  great  as  the  average 
turbidity  for  the  remaining  days. 

The  next  stream  is  a  considerable  creek  having  a  drainage  area 
of  350  square  miles.  The  observations  extended  over  117  days, 
during  which  time  there  were  seven  floods,  or  an  average  of  one 
flood  in  19  days.  The  floods  lasted  in  each  case  one  or  two  days, 
and  the  sum  of  the  turbidities  for  the  one  tenth  of  the  whole 
number  of  days  when  the  water  was  muddiest  was  55  per  cent  of 
the  aggregate  of  all  the  turbidities  for  the  period. 

The  last  case  is  that  ot  a  large  river,  with  a  drainage  area  of 
over  11,000  square  miles.  The  observations  extended  over  a  full 
year.  In  this  period  there  were  sixteen  floods,  each  lasting  from 
one  to  six  days,  and  the  sum  of  the  turbidities  for  the  one  tenth  of 
the  whole  number  of  days  when  the  water  was  muddiest  is  45  per 
cent  of  the  aggregate  turbidities  for  the  year.  The  floods  occurred 
on  an  average  of  once  in  22  days,  and  the  average  duration  was  two 
and  one  half  days. 

The  results  are  very  striking  as  showing  that  a  very  large  pro- 
portion of  the  mud  is  carried  by  the  water  in  flood  flows  of  com- 
paratively short  duration.  They  also  show  that  in  small  streams 
the  proportion  of  mud  in  the  flood-flows  is  greater,  and  the  average 
duration  of  floods  is  shorter,  than  in  larger  streams.  In  other 
words,  the  differences  between  flood-  and  low-water  flows  are 
greatest  in  small  streams,  and  gradually  become  less  as  the  size  of 
the  stream  increases. 

When  a  stream  is  used  for  water-works  purposes  in  the  usual 
-way,  a  certain  quantity  of  water  is  taken  from  the  stream  each 
day,  which  quantity  is  nearly  constant,  and  is  not  dependent  upon 


126  FILTRATION   OF  PUBLIC   WATER-SUPPLIES. 

the  condition  of  the  stream,  or  the  volume  of  its  flow.  The  pro- 
portions of  the  total  flows  taken  at  high-  and  low-water  stages  are 
very  different,  and  it  thus  happens  that  the  average  quality  of  the 
water  taken  for  water-works  purposes  is  different  from  the  average 
quality  of  all  the  water  flowing  in  the  stream. 

Let  us  assume,  for  example,  a  stream  having  a  watershed  of 
such  a  size  that  in  times  of  moderate  floods  water  from  the  most 
distant  points  reaches  the  water-works  intake  in  twenty-four 
hours.  Let  us  assume  further  that  rainfalls  of  sufficient  intensity 
to  cause  floods  and  muddy  water  occur,  on  an  average,  once  in  ten 
days,  and  that  the  turbidity  of  the  water  at  these  times  reaches 
l.oo,  and  that  for  the  rest  of  the  time  the  turbidity  averages  o.  10. 
Let  us  assume  further  that  at  times  of  storms  the  average  flow  of 
the  stream  is  100  units  of  volume,  and  for  the  nine  days  between 
storms  the  average  flow  is  10  units  of  volume.  We  shall  then 
have  in  a  ten  days'  period,  for  one  day,  100  volumes  of  water  with 
a  turbidity  of  i.OO,  and  nine  days  with  10  volumes  each,  or  a 
total  of  90  volumes  of  water  with  a  turbidity  of  o.  10.  The  total 
discharge  of  the  stream  will  then  be  190  volumes,  and  the  average 
turbidity  0.57.  The  turbidity  of  0.57  represents  the  average 
turbidity  of  all  the  water  flowing  in  the  stream,  or,  in  other  words, 
the  turbidity  which  would  be  found  in  a  lake  if  all  the  water  for 
ten  days  should  flow  into  it  and  become  thoroughly  mixed  without 
other  change. 

Now  let  us  compute  the  average  turbidity  of  the  water  taken 
from  the  stream  for  water-works  purposes.  The  water-works 
require,  let  us  say,  one  volume  each  day,  and  we  have  for  the  first 
day  water  with  a  turbidity  of  l.oo,  and  then  for  nine  days  water 
with  a  turbidity  of  o.  10.  The  average  turbidity  of  the  water 
taken  by  the  water-works  for  the  period  is  thus  only  0.19  in  place 
of  0.57,  the  average  turbidity  of  the  whole  run-off. 

The  average  turbidity  of  all  the  water  flowing  in  the  stream  is 
thus  three  times  as  great  as  that  of  the  water  taken  from  the 
stream  for  water-works  purposes. 


TURBIDITY  AND    COLOR.  12? 

It  is  often  noted  that  with  long  streams  the  water  becomes 
muddier  farther  down,  and  it  may  naturally  be  thought  that  it  is 
because  of  the  added  erosion  of  the  stream  upon  its  bed  in  its 
longer  course.  This,  of  course,  may  be  a  cause,  or  the  lower 
tributaries  may  be  muddier  than  the  upper  ones,  but  the  fact  that 
the  water  taken  at  the  lower  point  is  more  muddy  than  farther  up 
is  not  an  indication  of  this. 

Let  us  take,  for  example,  a  watershed  of  twice  the  size  of 
that  assumed  above,  that  is,  so  long  that  48  hours  will  be  required 
for  the  water  from  the  most  remote  feeders  to  reach  the  water- 
works intake.  Let  us  divide  this  shed  into  two  parts,  which  we 
will  assume  to  be  equal,  one  of  which  furnishes  water  reaching  the 
intake  within  24  hours,  and  the  other  water  reaching  the  intake 
between  24  and  48  hours.  Now  suppose  a  storm  upon  the  water- 
shed producing  turbidities  equal  to  those  just  assumed  for  the 
smaller  stream.  On  the  first  day  the  water  from  the  lower  half  of 
the  shed,  namely,  100  volumes  having  a  turbidity  of  i.oo,  passes 
the  intake,  but  this  is  mixed  with  10  volumes  of  water  from  the 
upper  half  of  the  watershed,  having  a  turbidity  of  o.  10,  and  the 
total  flow  is  thus  1 10  volumes  of  water  having  a  turbidity  of  0.92. 
On  the  second  day  the  water  from  the  lower  half  of  the  watershed 
has  returned  to  its  normal  condition,  and  the  flood-flow  of  the 
upper  half  of  the  watershed,  100  volumes  with  a  turbidity  of 
i.oo,  is  passing,  and  mingles  with  the  10  volumes  from  the  lower 
half  with  a  turbidity  of  o.  10,  and  the  total  flow  is  again  no 
volumes  having  a  turbidity  of  0.92.  The  following  eight  days, 
until  the  next  rain,  will  have  flows  of  20  volumes  each,  with 
turbidities  of  o.  10.  The  average  turbidity  of  all  of  the  water 
flowing  off  is  0.57  as  before,  but  the  water  taken  for  water-works 
purposes  will  consist  of  2  volumes  of  water  with  turbidities  of 
0.92,  and  8  volumes  with  turbidities  of  o.  10,  making  10  volumes 
with  an  average  turbidity  of  0.26. 

By  doubling  the  length  of  the  watershed  we  have  thus  doubled 
the  length  of  time  during  which  the  water  is  turbid,  and  have 


128  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

increased  the  average  turbidity  of  the  water  taken  for  water-works 
purposes  from  0.19  to  0.26,  although  the  average  turbidity  of  all 
the  water  running  off  remains  exactly  the  same. 

If  now  we  assume  a  watershed  so  long  that  three  days  are 
required  for  the  water  from  the  most  remote  points  to  reach  the 
intake,  with  computations  as  above,  water  taken  for  water-works 
purposes  will  have  an  average  turbidity  of  0.32;  and  with  still 
longer  watersheds  this  amount  will  increase,  until  with  a  water- 
shed so  long  that  ten  days,  or  the  interval  between  rains,  are 
required  for  the  water  from  the  upper  portions  to  reach  the  intake, 
the  average  turbidity  of  the  water  taken  for  water-works  purposes 
will  reach  the  average  turbidity  of  the  run-off,  namely,  0.57. 

In  the  above  computations  the  numbers  taken  are  round  ones, 
and  of  course  do  not  represent  closely  actual  conditions.  They 
do  serve,  however,  to  illustrate  clearly  the  principle  that  the 
larger  the  watershed,  other  things  being  equal,  the  more' mud  Jy 
will  be  the  water  obtained  from  it  for  water-works  purposes,  and 
the  longer  will  be  the  periods  of  muddy  water,  and  the  shorter 
the  periods  of  clear  water  between  them. 

It  cannot  be  too  strongly  emphasized  that  the  period  of  dura- 
tion of  muddy  water  is,  in  general,  dependent  upon  the  length  of 
time  necessary  for  the  muddy  water  to  run  out  of  the  stream 
system  after  it  is  once  in  it,  and  be  replaced  by  clear  water;  and 
that  the  settling  out  of  the  mud  in  the  river  has  very  little  to  do 
with  it. 

Muddy  waters  result  principally  from  the  action  of  rains  upon 
the  surface  of  ground  capable  of  being  washed,  and  the  turbidities 
of  the  stream  at  any  point  below  will  occur  at  the  times  when  the 
muddy  waters  reach  it  in  the  natural  course  of  flow,  and  will  dis- 
appear again  when  the  muddy  waters  present  in  the  stream  system 
at  the  end  of  the  rain  have  run  out,  and  have  been  replaced  with 
clear  water  from  underground  sources,  or  from  clearer  surface 
sources. 


TURBIDITY  AND    COLOR. 


THE   AMOUNTS    OF   SUSPENDED    MATTERS   IN   WATER. 


There  is  a  large  class  of  waters,  including  most  lake  and  reser- 
voir waters,  and  surface-waters  from  certain  geological  formations, 
which  are  almost  free  from  suspended  matters  and  turbidities. 
That  is  to  say,  the  average  turbidities  are  less  than  o.io,  and  the 
average  suspended  matters  are  less  than  2  parts  in  100,000,  and  are 
often  only  small  fractions  of  these  figures.  This  class  includes  the 
raw  waters  of  the  supplies  of  many  English  cities  drawn  from  im- 
pounding reservoirs,  and  also  the  waters  of  the  rivers  Thames  and 
Lea  at  London,  and  the  raw  waters  used  by  both  of  the  Berlin 
water-works,  and  in  the  United  States  the  waters  of  the  great 
lakes  except  at  special  points  near  the  mouths  of  rivers,  nearly  all 
New  England  waters,  and  many  other  waters  along  the  Atlantic 
coast  and  elsewhere  where  the  geological  formations  are  favorable. 

Data  regarding  the  suspended  matters  in  these  waters  are 
extremely  meagre.  The  official  examinations  of  the  London 
waters  contain  no  records  of  suspended  matters,  although  the 
clearness  of  filtered  waters  is  daily  reported.  Dibden,  in  his 
analytical  investigations  of  the  London  water-supply,  mentioned 
in  his  book  upon  '"  The  Purification  of  Sewage  and  Water," 
reports  the  average  suspended  matters  in  the  water  of  the  Thames 
near  the  water- works  intakes  as  0.77  part  in  100,000.  No 
figures  are  available  for  the  raw  waters  used  by  the  Berlin  water- 
works, but  both  are  taken  from  lakes,  and  are  generally  quite 
clear.  Even  in  times  of  floods  of  the  rivers  feeding  the  lakes, 
the  turbidities  are  not  very  high,  because  the  gathering  grounds 
for  the  waters  are  almost  entirely  of  a  sandy  nature,  yielding 
waters  with  low  turbidities,  and  further,  the  streams  flow  through 
successions  of  lakes  before  finally  reaching  the  lakes  from  which 
the  waters  are  taken.  It  is  safe  to  assume  that  the  suspended 
matters  and  turbidities  do  not  exceed  those  of  the  London  waters. 
Even  at  times  when  somewhat  turbid  water  is  obtained,  due  to 
agitation  by  heavy  winds,  the  suspended  matter  is  mainly  of  a 


130  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

sandy  nature,  readily  removed  by  settling,  and  it  does  not  seriously 
interfere  with  filtration. 

The  examinations  of  the  Massachusetts  State  Board  of  Health, 
with  a  very  few  exceptions,  contain  no  statements  of  suspended 
matters.  This  is  due  to  the  fact  that  the  suspended  matters,  in 
most  of  the  waters,  are  so  small  in  amount  as  to  make  them  hardly 
capable  of  determination  by  the  ordinary  gravimetric  processes, 
and  the  determinations  if  made  would  have  but  little  value.  The 
Merrimac  River  at  Lawrence,  at  the  time  of  the  greatest  flood  in 
fifty  years,  carried  silt  to  the  amount  of  about  1 1 1  parts  in 
100,000.  This  was  for  a  very  short  time,  and  the  suspended 
matter  consisted  almost  entirely  of  sand,  which  deposited  in  banks, 
the  deposited  sand  having  an  effective  size  of  0.04  or  0.05  mil- 
limeter. No  clayey  matter  is  ever  carried  in  quantity  by  the  river. 

The  reports  of  the  Connecticut  State  Board  of  Health  also 
contain  no  records  of  suspended  matters  for  the  same  reason.  It 
may  be  safely  said  that  the  average  suspended  matters  of  New 
England  waters  are  almost  always  less  than  I  part  in  100,000. 

Lake  waters  are  generally  almost  entirely  free  from  sediment. 
At  Chicago  the  city  water  drawn  from  Lake  Michigan  has  slightly 
more  than  I  part  in  100,000  of  suspended  matters,  as  determined 
by  Professor  Long  in  1888—9,  an(^  by  Professor  Palmer  in  1896.  The 
suspended  matter  in  this  case  is  probably  due  to  the  nearness  of 
the  intake  to  the  mouth  of  the  Chicago  River,  and  to  mud  brought 
up  from  the  bottom  in  times  of  storms.  The  lake-water  further 
away  from  the  shore  would  probably  give  much  lower  results. 

Turning  now  to  waters  having  considerable  turbidities,  at 
Pittsburg  the  average  suspended  matters  in  the  Allegheny  River 
water,  as  shown  by  the  weekly  or  semi-weekly  analyses  of  the 
Filtration  Commission  during  1897-8,  were  4  parts  in  100,000. 
During  a  large  part  of  the  time  the  suspended  matters  were  so 
small  that  it  was  not  deemed  worth  while  to  determine  them,  and 
the  results  are  returned  as  zero.  This  is  not  quite  correct,  and  a 
recomputation  of  the  amount  of  suspended  matters,  based  on  the 


TURBIDITY  AND    COLOR.  13* 

observed  amounts,  and  the  amounts  calculated  from  the  turbidities 
when  they  were  very  low,  leads  to  an  average  of  a  little  less  than 
5  parts  in  100,000,  which  is  probably  more  accurate  than  the  direct 
average.  The  average  turbidity  on  the  platinum-wire  scale  was 
o.  16. 

At  Cincinnati  the  suspended  matters  are  about  23  parts  in 
100,000,  and  at  Louisville  about  35  parts,  both  of  these  figures 
being  from  Mr.  Fuller's  reports.  In  all  these  cases  the  enormous 
and  rapid  fluctuations  in  the  turbidity  of  the  water  is  a  most 
striking  feature  of  the  results. 

Observations  on  the  Mississippi  River  above  the  Ohio  have 
been  made  by  Professor  Long  in  1888—9,  anc^  by  Professor  Palmer 
in  1896.  These  results  are  not  as  full  and  systematic  as  could  be 
desired,  but  indicate  averages  of  20  to  30  parts  in  100,000  at 
the  different  points.  Professor  William  Ripley  Nichols,  in  his, 
work  on  water-supply,  states  the  amount  of  suspended  matter  in 
the  water  of  the  Mississippi,  probably  referring  to  the  lower  river^ 
as  66.66  parts. 

Investigations  of  Professor  Long  and  Professor  Palmer  for 
numerous  interior  Illinois  streams  extending  over  considerable 
periods  give  average  results  ranging  from  I  to  8  parts  in  100,000. 
The  very  much  lower  results  for  the  interior  streams  as  compared 
with  the  Mississippi  and  Ohio  rivers  may  be  due  to  the  relative 
sizes  and  lengths  of  the  streams,  or  in  part  to  other  causes. 

Regarding  muddy  European  rivers  there  are  but  few  data. 
The  Maas,  used  for  the  water-supply  of  Rotterdam,  is  reported  by 
Professor  Nichols  as  having  from  1.40  to  47.61  and  averaging  10 
parts  of  suspended  matters  in  100,000.  More  recent  information 
is  to  the  effect  that  the  raw  water  has  at  most  30  parts  of  sus- 
pended matters,  and  that  that  quantity  is  very  seldom  reached. 

At  Bremen  the  Weser  often  becomes  quite  turbid.  The 
turbidity  of  the  water  is  noted  every  day  by  taking  the  depth  at 
which  a  black  line  on  a  white  surface  can  be  seen.  Assuming  that 
this  procedure  is  equivalent  to  the  platinum-wire  procedure,  the 


132  FILTRATION   OF  PUBLIC   WATER-SUPPLIES, 

depths  at  which  the  wire  can  be  seen,  namely,  from  15  to  600 
millimeters,  correspond  to  turbidities  of  from  0.04  to  1.70,  a  result 
not  very  different  from  the  conditions  at  Pittsburg. 

At  Hamburg  and  Altona  the  water  is  generally  tolerably  clear, 
but  at  times  of  flood  the  Elbe  becomes  very  turbid,  and  the 
^amount  of  mud  deposited  in  the  sedimentation-basins  is  consider- 
able. At  Dresden,  several  hundred  miles  up  the  river,  I  have 
repeatedly  seen  the  river-water  extremely  turbid  with  clayey  mat- 
ter, the  color  of  the  clay  varying  from  day  to  day,  corresponding 
to  the  color  of  the  earth  from  which  it  had  been  washed. 

At  Budapest,  where  filters  were  used  temporarily,  the  Danube 
water  was  excessively  muddy"  with  clayey  material.  At  first  very 
high  rates  of  filtration  were  employed  and  the  results  were  not 
satisfactory.  Afterward  the  rate  of  filtration  was  limited  to  1.07 
million  gallons  per  acre  daily,  and  good  results  were  secured. 
There  was  no  preliminary  sedimentation.  Professor  Nichols  re- 
ports the  average  suspended  matters  in  the  Danube  at  32.68  parts 
in  100,000,  but  does  not  state  at  what  place. 

Many  of  the  French  and  German  rivers  drain  prairie  country 
not  different  in  its  general  aspect  from  the  Mississippi  basin,  and 
the  soil  is  probably  in  many  places  similar.  There  is  no  reason 
to  suppose  that  the  turbidities  of  these  streams  in  general  are 
materially  different  from  those  of  corresponding  streams  in  the 
United  States,  although  it  is  true  that,  other  things  being  equal, 
the  average  turbidity  of  water  taken  for  water-works  purposes  will 
increase  with  the  size  of  the  stream;  and  it  maybe  that  some 
American  streams,  especially  the  Ohio,  Missouri,  and  Mississippi 
rivers,  are  of  larger  size  than  European  streams,  and  consequently 
that  the  turbidity  of  the  water  taken  from  them  for  water-works 
purposes  may  be  greater. 

The  following  are  the  drainage  areas  of  a  number  of  European 
and  American  streams  yielding  more  or  less  muddy  waters  at 
points  where  they  are  used  for  public  water-supplies  after  filtra- 
tion, with  a  few  other  American  points  for  comparison.  The 


TURBIDITY  AND    COLOR. 


133 


results  are  obtained  in  most  cases  from  measurements  of  the  best 
available  maps. 


Place. 

River. 

Drainage  Area, 
Square  Miles. 

New  Orleans    La   

Mississippi  • 

St.  Louis,  Mo  

7OO  OOO 

St    Petersburg  

Neva  

Rock  Island    111  

88  ooo 

Budapest     • 

Ohio     .        

79,000 

Maas  

75,700 
68  ooo 

Rotterdam   

68  ooo 

Schiedam  

,4 

68  ooo 

Elbe  

52  ooo 

Oder     

Elbe  

36  ooo 

Weichsel 

Odessa  

J4,uoo 

26  ooo 

\Vorms         

Rhine     .             .... 

Grand  Forks    N    Dak    .... 

Red  River  of  the  North 

Oder  

21  OOO 

Bremen  

Weser  

15  ooo 

12  OOO 

1  1  600 

II  400 

Wartha  

9J.OO 

Hudson    N    Y 

H  udson 

Albany    N    Y   

8  200 

Breslau....          

Oder     

8  200 

Brieg  

7  coo 

Lawrence    Mass         

Merrimac   

A     O7J. 

Neckar  

I  660 

Ocker  

650 

Somersworth    N    H             . 

171 

PRELIMINARY    PROCESSES   TO    REMOVE    MUD. 

With  both  sand  and  mechanical  filtration  the  difficulty  and 
expense  of  treatment  of  a  water  increase  nearly  in  direct  propor- 
tion to  the  turbidity  of  the  water  as  applied  to  the  filter;  and  it  is 
thus  highly  important  to  secure  a  water  for  filtration  with  as  little 
turbidity  as  possible,  and  thus  to  develop  to  their  economical 
limits  the  preliminary  processes  for  the  removal  of  mud.  One  of 
the  most  important  of  these  processes  is  the  use  of  reservoirs. 

Reservoirs  serve  two  purposes  in  connection  with  waters  drawn 


134  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

from  streams:  they  allow  sedimentation,  and  they  afford  storage. 
If  a  water  having  a  turbidity  of  i.oo  is  allowed  to  remain  in  a 
sedimentation-basin  for  24  hours,  its  turbidity  may  be  reduced  by 
as  much  as  40  per  cent,  or  to  0.60.  If  it  is  held  a  second  day 
the  additional  reduction  is  much  less. 

If  samples  are  taken  of  the  water  in  the  reservoir  before  and 
after  settling  and  sent  to  the  chemist  for  analysis,  he  will  probably 
report  that  from  70  to  80  per  cent  of  the  suspended  matters  have 
been  removed  by  the  process.  The  suspended  matters  are  re- 
moved in  much  larger  ratio  than  the  turbidity.  This  arises  from 
the  fact  that  there  is  a  certain  proportion  of  comparatively  coarse 
material  in  the  water  as  it  is  taken  from  the  river.  This  coarse 
material  increases  the  weight  of  the  suspended  matters  without 
increasing  the  turbidity  in  a  corresponding  degree.  In  24  hours 
the  coarser  materials  are  removed  completely,  and  at  the  end  of 
that  time  only  the  clayey  or  finer  particles  remain  in  suspension. 
It  is  these  clayey  particles,  however,  that  constitute  the  turbidity, 
ivhich  are  most  objectionable  in  appearance,  and  which  are  most 
difficult  of  removal  by  filtration  or  otherwise. 

Sedimentation  thus  removes  the  heavier  matters  from  the 
water,  but  it  does  not  remove  the  finer  matters  which  principally 
affect  the  appearance  of  the  water  and  are  otherwise  most  trouble- 
some. A  sedimentation  of  24  hours  removes  practically  all  of  the 
coarser  matters,  and  the  clayey  material  remaining  at  the  end  of 
that  time  can  hardly  be  removed  by  further  sedimentation.  The 
economic  limit  of  sedimentation  is  about  24  hours. 

Sedimentation  has  practically  no  effect  upon  the  clearer  waters 
between  flood  periods. 

Let  us  consider  the  effect  of  a  sedimentation-basin,  or  reservoir 
holding  a  24-hours'  supply  of  water,  into  which  water  is  constantly 
pumped  at  one  end,  and  from  which  an  equal  quantity  is  con- 
stantly withdrawn  from  the  other,  upon  the  water  of  a  stream  of 
such  size  that  the  time  of  passage  of  water  from  the  feeders  to  the 
intake  is  less  than  24  hours.  During  the  period  between  storms 


TURBIDITY  AND    COLOR.  135 

the  water  is  comparatively  clear  and  passes  through  the  sedimen- 
tation basin  without  change.  When  a  storm  comes  the  water  in 
the  stream  promptly  becomes  muddy,  and  muddy  water  is  sup- 
plied to  the  reservoir;  but  owing  to  the  time  required  for  water 
to  pass  through  it,  the  outflowing  water  remains  clear  for  some 
hours.  There  is  a  gradual  mixing,  however,  and  long  before  the 
expiration  of  24  hours  somewhat  muddy  water  appears  at  the 
outlet.  The  turbid-water  period  rarely  lasts  in  streams  of  this 
size  more  than  24  hours,  and  at  the  expiration  of  that  time  the 
water  in  the  sedimentation-basin  is  as  muddy  or  muddier  than  the 
water  flowing  in  the  stream.  After  the  height  of  the  flood  the 
stream  clears  itself  by  the  flowing  away  of  the  turbid  water  much 
more  rapidly  than  the  water  clears  itself  by  sedimentation  in  the 
reservoir.  That  is  to  say,  if  at  the  time  of  maximum  turbidity 
we  take  a  certain  quantity  of  water  from  the  stream  and  put  it 
aside  to  settle,  at  no  time  will  the  improvement  by  settling  equal 
the  improvement  which  has  taken  place  in  the  stream  from  natural 
causes.  Generally  the  improvement  in  the  stream  is  several  times 
as  rapid  as  in  the  sedimentation-basin,  and  the  water  from  it  will 
at  times  have  only  a  fraction  of  the  turbidity  of  the  water  in  the 
basin. 

Let  us  now  consider  what  the  sedimentation  has  done  to  im- 
prove the  water.  During  the  period  of  clear  water,  that  is  for  most 
of  the  time,  it  has  done  nothing.  For  the  first  day  of  each  flood 
period  very  much  clearer  water  has  been  obtained  from  it  than  was 
flowing  in  the  stream.  For  the  first  days  following  floods  the  water 
in  the  sedimentation-basin  has  been  more  muddy  than  the  water 
in  the  stream.  The  only  time  when  the  sedimentation-basin  has 
been  of  use  is  during  the  first  part  of  floods,  that  is,  when  the 
turbidity  of  the  water  in  the  stream  is  increasing.  During  this 
period  it  has  been  of  service  principally  because  of  its  storage 
capacity,  yielding  up  water  received  from  the  stream  previously, 
when  it  was  less  muddy.  Such  sedimentation  as  has  been  secured 
is  merely  incidental  and  generally  not  important  in  amount. 


136  FIL7^RAT2ON  OF  PUBLIC    WATER-SUPPLIES. 

It  will  be  obvious  from  the  above  that  for  these  conditions 
storage  is  much  more  important  than  sedimentation.  This  brings 
us  back  to  the  old  English  idea  of  having  storage-reservoirs  large 
enough  to  carry  water-works  over  flood  periods  without  the  use  of 
flood-waters.  Reservoirs  of  this  kind  were,  and  still  are,  consid- 
ered necessary  for  the  successful  utilization  of  waters  of  many 
English  rivers,  although  these  waters  do  not  approach  in  turbidity 
the  waters  of  some  American  streams.  This  idea  of  storage  has 
been  but  little  used  in  the  United  States. 

In  the  above  case,  if  we  use  our  reservoir  for  storage  instead 
of  as  a  sedimentation-basin,  the  average  quality  of  the  water  can 
be  greatly  improved.  The  reservoir  should  ordinarily  be  kept 
full,  and  pumping  to  it  should  be  stopped  whenever  the  turbidity 
exceeds  a  certain  limit,  to  be  determined  by  experience;  and  the 
reservoir  is  then  to  be  drawn  upon  for  the  supply  until  the 
turbidity  again  falls  to  the  normal.  In  the  case  assumed  above, 
with  a  stream  in  which  all  of  the  water  reaches  the  intake  in  24 
hours,  a  reservoir  holding  a  24-hours'  supply,  or  in  practice,  to  be 
safe,  a  somewhat  larger  one,  would  yield  a  water  having  a  very 
much  lower  average  turbidity  than  would  be  obtained  with  water 
pumped  constantly  from  the  stream  without  a  reservoir. 

With  a  river  having  a  watershed  so  long  that  48  hours  are 
required  to  bring  the  water  down  from  the  most  remote  feeders,  a 
reservoir  twice  as  large  would  be  required,  and  would  result  in  a 
still  greater  reduction  in  the  average  turbidity. 

As  the  stream  becomes  larger,  and  the  turbid  periods  longer, 
the  size  of  a  reservoir  necessary  to  utilize  this  action  rapidly 
becomes  larger,  and  the  times  during  which  it  can  be  filled  are 
shortened,  and  thus  the  engineering  difficulties  of  the  problem  are 
increased.  For  moderately  short  streams,  cost  for  cost,  storage 
is  far  more  effective  than  sedimentation,  and  we  must  come  back 
to  the  old  English  practice  of  stopping  our  pumps  during  periods 
of  maximum  turbidity. 


TURBIDITY  AND    COLOR.  137 

EFFECT   OF   MUD    UPON   SAND    FILTERS. 

There  are  two  aspects  of  the  effect  of  mud  upon  the  operation 
of  sand  filters  which  require  particular  consideration.  The  first 
relates  to  the  rapidity  of  clogging,  and  consequently  the  frequency 
of  scraping  and  the  cost  of  operation;  while  the  second  relates  to 
the  ability  of  the  filters  to  yield  well-clarified  effluents. 

EFFECT    OF   TURBIDITY    UPON   THE    LENGTH    OF    PERIOD. 

The  amount  of  water  which  can  be  filtered  between  scrapings 
is  directly  dependent  upon  the  turbidity  of  the  raw  water.  The 
greater  the  turbidity,  the  more  frequently  will  filters  require  to  be 
scraped.  In  the  experiments  of  the  Pittsburg  Filtration  Commis- 
sion, with  4  feet  of  sand  of  an  effective  size  of  about  0.30  mil- 
limeter, and  with  rates  of  filtration  of  about  three  million  gallons 
per  acre  daily,  and  with  the  loss  of  head  limited  to  4  feet, 
sand  filters  were  operated  as  follows:  For  five  periods  the  turbidi- 
ties of  the  raw  water  ranged  from  0.035  to  0.062,  and  averaged 
0.051,  and  the  corresponding  periods  ranged  from  102  to  136,  and 
averaged  113  million  gallons  per  acre  filtered  between  scrapings, 
For  ten  periods  the  turbidities  of  the  raw  water  ranged  from  0.079 
to  0.128,  and  averaged  0.102,  and  the  periods  averaged  78  million 
gallons  per  acre  between  scrapings.  For  fifteen  other  periods  the 
turbidities  of  the  raw  water  ranged  from  0.134  to  0.269,  and 
averaged  0.195,  and  the  periods  averaged  52  million  gallons  per 
acre  between  scrapings.  In  two  other  periods  the  turbidities  of  the 
raw  water  averaged  0.67,  and  the  periods  between  scrapings 
averaged  16  million  gallons.  In  all  cases  the  turbidity  is  taken 
as  that  of  the  water  applied  to  the  filter.  Usually  this  was  the 
turbidity  of  the  settled  water,  but  in  some  cases  raw  water  was 
applied,  and  in  these  case  the  turbidity  of  the  raw  water  is  taken. 
These  results  are  approximately  represented  by  the  formula 

Period  between  scrapings,  )  12 


million  gallons  per  acre     )  "~  turbidity  +  0.05 


- 


138  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

Except  for  very  clear  waters  the  amount  of  water  passed  between 
scrapings  is  nearly  inversely  proportional  to  the  turbidity.  With 
twice  as  great  an  amount  of  turbidity,  filters  will  have  to  be  cleaned 
twice  as  often,  the  reserve  area  for  cleaning  will  require  to  be 
twice  as  great,  and  the  cost  of  scraping  filters  and  of  washing  and 
replacing  sand,  which  is  the  most  important  element  in  the  cost 
of  operation,  will  be  doubled. 

With  waters  having  turbidities  of  0.20  upon  this  basis,  the 
average  period  will  be  about  5 1  million  gallons  per  acre  between 
scrapings.  This  is  about  the  average  result  obtained  at  the 
German  works  filtering  river  waters,  and  there  is  no  serious  diffi- 
culty in  operating  filters  which  require  to  be  scraped  with  this 
frequency.  With  more  turbid  waters  the  period  is  decreased. 
With  an  average  turbidity  of  0.50  the  average  period  is  only  24 
million  gallons  per  acre  between  scrapings,  a  condition  which 
means  very  difficult  operation  and  a  very  high  cost  of  cleaning. 
With  much  more  turbid  waters  the  difficulties  are  increased,  and 
if  the  duration  of  turbid  water  should  be  long-continued,  the 
operation  of  sand  filters  would  clearly  be  impracticable,  and  the 
expense,  also,  would  be  prohibitive. 

In  applying  these  figures  to  actual  cases  it  must  be  borne  in 
mind  that  the  turbidity  is  only  one  of  the  several  factors  which 
control  the  length  of  period ;  and  that  the  turbidity  of  a  water  of 
a  given  stream  is  never  constant,  but  fluctuates  within  wide  limits; 
and  that  raw  water  can  be  applied  to  filters  for  a  short  time  with- 
out injurious  results,  even  though  it  is  so  turbid  that  its  continued 
application  would  be  fatal. 

It  is  very  likely  also  that  the  suspended  matters  in  different 
streams  differ  in  their  natures  to  such  an  extent  that  equal  turbidi- 
ties would  give  quite  different  periods,  although  the  Pittsburg  results 
were  so  regular  as  to  give  confidence  in  their  application  to  other 
conditions  within  reasonable  limits,  and  when  so  applied  they  afford 
a  most  convenient  method  of  computing  the  approximate  cost  of 
operation  of  filters  for  waters  of  known  or  estimated  turbidities. 


EFFECT   OF  MUD    UPON  SAND    FILTERS.  139 

POWER  OF   SAND    FILTERS   TO    PRODUCE  CLEAR    EFFLUENTS    FROM 

MUDDY    WATER. 

When  the  turbidity  of  the  applied  water  is  not  too  great  it  is 
entirely  removed  in  the  course  of  filtration.  With  extremely 
muddy  raw  waters,  however,  turbid  effluents  are  often  produced 
with  sand  filters.  The  conditions  which  control  the  passage  of 
the  finest  suspended  matters  through  filters  have  been  studied  by 
Mr.  Fuller  at  Cincinnati  at  considerable  length.  They  are  similar 
in  a  general  way  to  the  conditions  which  control  the  removal  of 
bacteria.  That  is  to  say,  the  removal  is  more  complete  with  fine 
filter  sand  than  with  coarse  sand;  with  a  deep  sand  layer  than 
with  a  shallow  sand  layer;  and  with  low  rates  of  filtration  than 
with  high  rates.  The  practicable  limits  to  the  size  of  sand  grain, 
depth  of  sand  layer,  and  rate  of  filtration  are  established  by  other 
conditions,  and  the  question  remains  whether  within  these  limits 
a  clear  effluent  can  be  produced. 

At  Pittsburg  the  turbidity  of  the  effluent  from  a  sand  filter 
operated  as  mentioned  above,  which  received  water  which  had 
passed  through  a  sedimentation-basin  holding  about  a  24-hours' 
supply,  but  without  taking  any  advantage  of  storage  to  avoid  the 
use  of  muddy  water,  was  nearly  always  less  than  0.02,  which  may  be 
taken  as  the  admissible  limit  of  turbidity  in  a  public  water-supply. 
This  limit  was  exceeded  on  less  than  20  days  out  of  365,  these 
days  being  during  the  winter  and  spring  freshets,  and  on  these  days 
the  excess  was  not  such  as  would  be  likely  to  be  particularly 
objectionable.  For  the  water  of  the  Allegheny  River,  then,  sand 
filtration  with  one  day's  sedimentation  is  capable  of  yielding  a 
water  not  absolutely  clear,  but  sufficiently  clear  to  be  quite  satis- 
factory for  the  purpose  of  municipal  water-supply. 

At  Cincinnati,  on  the  other  hand,  where  the  amount  of  sus- 
pended matters  was  five  times  as  great  as  at  Pittsburg,  the 
effluents  which  could  be  obtained  by  sand  filtration  without 
recourse  to  the  use  of  alum,  even  under  most  favorable  conditions, 


140  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

were  very  much  more  turbid  than  those  obtained  at  Pittsburg,  and 
were,  in  fact,  so  turbid  as  to  be  seriously  objectionable  for  the 
purpose  of  public  water-supply. 

With  rivers  no  more  turbid  than  the  Allegheny  River  at  Pitts- 
burg,  and  rivers  having  floods  of  such  short  duration  that  the  use 
of  flood-flows  can  be  avoided  by  the  use  of  reservoirs,  sand  filters 
are  adequate  for  clarification.  For  waters  which  are  much  muddier 
than  the  Allegheny,  as,  for  instance,  the  Ohio  at  Cincinnati  and  at 
Louisville,  sand  filtration  alone  is  inadequate.  Mr.  Fuller,*  as  a 
result  of  his  Cincinnati  experiments,  has  stated  the  case  as  follows: 

"  For  the  sake  of  explicitness  it  is  desired  to  show,  with  the 
data  of  the  fairly  normal  year  of  1898,  the  proportion  of  the  time 
when  English  filters  (that  is,  sand  filters)  would  be  inapplicable  in 
the  purification  of  the  unsubsided  Ohio  River  water  at  Cincinnati. 
This  necessitates  fixing  an  average  limit  of  permissible  suspended 
matter  in  this  river  water,  and  is  a  difficult  matter  from  present 
evidence. 

"  In  part  this  is  due  to  variations  in  the  character  and  in  the 
relative  amounts  of  the  suspended  silt,  clay,  and  organic  matter; 
and  in  part  it  is  due  to  different  amounts  of  clay  stored  in  the  sand 
layer,  which  affects  materially  the  capacity  of  the  filter  to  retain 
the  clay  of  the  applied  water.  During  these  investigations  the 
unsubsided  river-water  was  not  regularly  applied  to  filters;  and, 
with  the  exception  of  the  results  of  tests  for  a  few  days  only,  it  is 
necessary  to  depend  upon  general  information  obtained  with  refer- 
ence to  this  point.  So  far  as  the  information  goes,  it  appears  that 
an  average  of  125  parts  per  million  is  a  conservative  estimate  of 
the  amount  of  suspended  matters  in  the  unsubsided  river-water, 
which  could  be  regularly  and  satisfactorily  handled  by  English 
filters.  But  at  times  this  estimated  average  would  be  too  low, 
and  at  other  times  too  high.  .  .  . 

"  While  English  filters  are  able  to  remove  satisfactorily  on  an 

*  Report  on  Water  Purification  at  Cincinnati,  page  378. 


EFFECT   OF  MU£>    UPON  SAND   fILTERS.  14! 

average  about  125  parts  of  silt  and  clay  of  the  unsubsided  water, 
actual  experience  shows  that  they  can  regularly  handle  suspended 
clay  in  subsided  water  in  amounts  ranging  only  as  high  as  from 
30  to  70  parts  (depending  upon  the  amount  of  the  clay  stored  in 
the  sand  layer),  and  averaging  about  50  parts  per  million.  But  it 
is  true  that  for  two  or  three  days  on  short  rises  in  the  river,  or  at 
the  beginning  of  long  freshets,  the  retentive  capacity  of  the  sand 
layer  allows  of  satisfactory  results  with  the  clay  in  the  applied 
water  considerably  in  excess  of  70  parts.  If  this  capacity  is 
greatly  overtaxed,  however,  the  advantage  is  merely  temporary, 
as  the  stored  clay  is  washed  out  later,  producing  markedly  turbid 
effluents." 

Translating  Mr.  Fuller's  results  into  terms  of  turbidity,  the 
125  parts  per  million  of  suspended  matters  in  the  raw  water  repre- 
sent a  turbidity  of  about  0.40,  and  the  30  to  70  parts  of  suspended 
matters  in  the  settled  water  represent  turbidities  from  0.20  to 
0.40,  the  average  of  50  parts  of  suspended  matters  corresponding 
to  a  turbidity  of  about  0.30. 

Upon  this  basis,  then,  sand  filters  are  capable  of  treating  raw 
waters  with  average  turbidities  up  to  0.40,  or  settled  waters  with 
average  turbidities  up  to  0.30,  but  waters  more  turbid  than  this 
are  incapable  of  being  successfully  treated  without  the  use  of 
coagulants  or  other  aids  to  the  process.  These  results  are  in 
general  accordance  with  the  results  of  the  experiments  at  Pitts- 
burg,  and  demonstrate  that  while  sand  filters  as  generally  used  in 
Europe  are  adequate  for  the  clarification  of  many,  if  not  most, 
river  waters  in  the  United  States,  there  are  other  waters  carrying 
mud  in  such  quantities  as  to  make  the  process  inapplicable  to 
them. 


EFFECT   OF   MUD    UPON   BACTERIAL   EFFICIENCY   OF   FILTERS. 

The  question  is  naturally  raised  as  to  whether  or  not  the  pres 
ence  of  large  quantities  of  mud  in  the  raw  water  will  not  seriously 


I42  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

interfere  with  the  bacterial  efficiency  of  filters.  Experiments  at 
Cincinnati  and  Pittsburg  have  given  most  conclusive  and  satisfac- 
tory information  upon  this  point.  Up  to  the  point  where  the 
effluents  become  quite  turbid,  the  mud  in  the  raw  water  has  no 
influence  upon  the  bacterial  efficiency;  and  even  somewhat  beyond 
this  point,  with  effluents  so  turbid  that  they  would  hardly  be  suit- 
able for  the  purpose  of  a  public  water-supply,  the  bacterial  efficiency 
remains  substantially  equal  to  that  obtained  with  the  clearest 
waters.  Only  in  the  case  of  excessive  quantities  of  mud,  where, 
for  other  reasons,  sand  filters  can  hardly  be  considered  applicable, 
is  there  a  moderate  reduction  in  bacterial  efficiency.  As  men- 
tioned above,  particles  constituting  turbidity  are  often  much 
smaller  than  the  bacteria,  and  in  addition,  the  bacteria  probably 
have  an  adhesive  power  far  in  excess  of  that  of  the  clay  particles. 
For  these  reasons  clay  particles  are  able  to  pass  filters  under  con- 
ditions which  almost  entirely  prevent  the  passage  of  bacteria. 

On  the  other  hand,  it  does  not  necessarily  follow  that  the 
removal  of  turbidity  is  accompanied  by  high  bacterial  efficiency. 
Although  this  is  often  the  case,  there  are  marked  exceptions, 
particularly  in  connection  with  the  use  of  coagulants,  where  very 
good  clarification  is  obtained,  and  notwithstanding  this,  effluents 
are  produced  containing  comparatively  large  numbers  of  bacteria. 

LIMITS   TO    THE    USE    OF    SUBSIDENCE    FOR   THE    PRELIMINARY 
TREATMENT    OF    MUDDY    WATERS. 

When  water  is  too  muddy  to  be  applied  directly  to  filters,  the 
most  obvious  treatment  is  to  remove  as  much  of  the  sediment  as 
possible  by  sedimentation.  Sedimentation-basins  are  considered 
as  essential  parts  of  filtration  plants  for  the  treatment  of  muddy 
waters.  The  effect  of  sedimentation,  as  noted  above,  is  to 
remove  principally  the  larger  particles  in  the  raw  water.  By  doing 
this  the  deposit  upon  the  surface  of  the  filters  and  the  cost  of 
operation  are  greatly  reduced. 

These  larger  particles  are  mainly  removed  by  a  comparative!/ 


EFFECT  OF  MUD    UPON  SAND    FILTERS.  143 

short  period  of  sedimentation,  and  the  improvement  effected  after 
the  first  24  hours  is  comparatively  slight.  The  particles  remain- 
ing in  suspension  at  the  end  of  this  time  consist  almost  entirely  of 
very  fine  clay,  and  the  rate  of  their  settlement  through  the  water 
is  extremely  slow;  and  currents  in  the  basin,  due  to  temperature 
changes,  winds,  etc.,  almost  entirely  offset  the  natural  tendency 
of  the  sediment  to  fall  to  the  bottom. 

There  is  thus  a  practical  limit  to  the  effect  of  sedimentation 
which  is  soon  reached,  and  it  has  not  been  found  feasible  to 
extend  the  process  so  as  to  allow  much  more  turbid  waters  to  be 
brought  within  the  range  which  can  be  economically  treated  by 
sand  filtration. 


144  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


CHAPTER    IX. 
THE   COAGULATION   OF   WATERS. 

THE  coagulation  of  water  consists  in  the  addition  to  it  of  some 
substance  which  forms  an  inorganic  precipitate  in  the  water,  the 
presence  of  which  has  a  physical  action  upon  the  suspended 
matters,  and  allows  them  to  be  more  readily  removed  by  subsi- 
dence or  filtration. 

The  most  common  coagulant  is  sulphate  of  alumina.  When 
this  substance  is  added  to  water  it  is  decomposed  into  its  com- 
ponent parts,  sulphuric  acid  and  alumina,  the  former  of  which 
combines  with  the  lime  or  other  base  present  in  the  water,  or  in 
case  enough  of  this  is  lacking,  it  remains  partly  as  free  acid  and 
partly  undecomposed  in  its  original  condition;  while  the  alumina 
forms  a  gelatinous  precipitate  which  draws  together  and  surrounds 
the  suspended  matters  present  in  the  water,  including  the  bacteria, 
and  allows  them  to  be  much  more  easily  removed  by  filtration 
than  would  otherwise  be  the  case.  In  addition,  the  alumina  has  a 
chemical  attraction  for  dissolved  organic  matters,  and  the  chemical 
purification  may  be  more  complete  at  very  high  rates  than  would 
be  possible  with  sand  filtration  without  coagulant  at  any  rate, 
however  low. 

Coagulants  have  been  employed  in  connection  with  filtration 
from  very  early  times.  As  early  as  1831  D'Arcet  published  in  the 
"  Annales  d'hygiene  publique,"  *  an  account  of  the  purification 
of  Nile  water  in  Egypt  by  adding  alum  to  the  water,  and  afterwards 
filtering  it  through  small  household  filters.  More  recently  alum 
has  been  repeatedly  used  in  connection  with  sand  filters,  particu- 

*  Translation  in  German  in  Dingler's  Polytechnical  Journal,  1832,  386. 


THE    COAGULATION  OF   WATERS.  145 

larly  at  Leeuwarden,  Groningen,  and  Schiedam  in  Holland,  where 
the  river  waters  used  for  public  supplies  are  colored  by  peaty 
matter  which  cannot  be  removed  by  simple  filtration. 

SUBSTANCES    USED    FOR   COAGULATION. 

Mr.  Fuller*  has  given  a  very  full  account  of  the  substances 
which  can  be  used  for  the  clarification  of  waters.  Without  taking 
up  all  of  the  unusual  substances  which  have  been  suggested,  the 
most  important  of  the  coagulants  will  be  briefly  described  below. 

Lime. — Lime  has  been  extensively  used  in  connection  with  the 
purification  of  sewage,  and  also  for  softening  water.  Lime  is  first 
slaked  and  converted  into  calcium  hydrate,  which  is  afterwards 
dissolved  in  water,  and  applied  to  the  water  under  treatment. 
The  amount  of  lime  to  be  used  is  fixed  by  the  amount  of  carbonic 
acid  in  the  water.  So  much  lime  is  always  used  as  will  exactly 
convert  the  whole  of  the  carbonic  acid  of  the  water  into  normal 
carbonate  of  lime.  This  substance  is  but  slightly  soluble  in  water 
and  it  precipitates.  The  precipitate  is  crystalline  rather  than 
flocculent,  and  is  not  as  well  adapted  to  aid  in  the  removal  of  clayey 
matters  as  some  other  substances,  although  its  action  in  this 
respect  is  considerable.  The  precipitate  is  quite  heavy,  and  is 
largely  removed  by  sedimentation,  although  filtration  must  be 
used  to  complete  the  process.  Water  which  has  been  treated  with 
lime  is  slightly  caustic;  that  is  to  say,  there  is  a  deficiency  of 
carbonic  acid  in  it,  and  it  deposits  lime  in  the  pipes,  in  pumps, 
etc. ;  and  although  the  precipitated  calcium  carbonate  is  much 
softer  than  steel,  it  rapidly  destroys  pumps  used  for  lifting  it. 

Principally  for  these  reasons  it  is  necessary  to  supply  carbonic 
acid  to  water  which  has  been  treated  in  this  way,  and  this  is  done 
by  bringing  it  in  contact  with  flue-gases,  or  by  the  direct  addition 
of  carbonic  acid. 

The  use  of  lime  for  softening  waters  is  known  as  Clark's 
process.  It  was  patented  in  England  many  years  ago,  and  the 

*  Water  Purification  at  Louisville,  page  378. 


146  FILTRA7'JON  OF  PUBLIC    WATER-SUPPLIES. 

patent  has  now  expired.  Various  ingenious  devices  have  been 
constructed  for  facilitating  various  parts  of  the  operation.  The 
process  has  hardly  been  used  in  the  United  States,  but  there  is  a 
large  field  for  it  in  connection  with  the  softening  of  very  hard 
waters,  and  where  such  waters  also  contain  iron  or  clay,  these 
substances  will  be  incidentally  removed  by  the  process. 

Larger  quantities  of  lime  have  an  action  upon  the  suspended 
matters  which  is  entirely  different  from  that  secured  in  Clark's 
process,  and  the  action  upon  bacteria  is  particularly  noteworthy. 
This  action  was  noted  in  experiments  at  Lawrence,*  where  it  was 
found  that  sewage  was  almost  completely  sterilized  by  the  applica- 
tion of  considerable  quantities  of  lime.  An  extremely  interesting 
series  of  experiments  upon  the  application  of  large  quantities  of 
lime  to  water  was  made  by  Mr.  Fuller  in  1899:^  The  bacterial 
results  were  extremely  favorable,  although  the  necessity  for  remov- 
ing the  excess  of  lime  afterward  is  a  somewhat  serious  matter,  and 
in  these  experiments  it  was  not  entirely  accomplished. 

Aluminum  Compounds.* — Sulphate  of  alumina  is  most  commonly 
employed.  It  can  be  obtained  in  a  state  of  considerable  purity  at 
a  very  moderate  price,  and  important  improvements  in  the 
methods  used  for  its  manufacture  have  been  recently  introduced. 
Potash  and  soda  alums  have  no  advantage  over  sulphate  of  alumina, 
and,  in  fact,  are  less  efficient  per  pound,  while  their  costs  are 
greater.  Chloride  of  alumina  is  practically  equivalent  to  the  sul- 
phate in  purifying  power,  but  is  more  expensive. 

Sodium  Aiuminate  has  been  examined  by  Mr.  Fuller,  who 
states  that  experience  has  shown  that  its  use  is  impracticable  in 
the  case  of  the  Ohio  River  water. 

Compounds  of  Iron. — Iron  forms  two  classes  of  compounds, 
namely,  ferrous  and  ferric  salts.  When  the  ferrous  salts  are 
applied  to  water,  under  certain  conditions,  ferrous  hydrate  is  pre- 

*  Special   Report  Mass.  State  Board  of  Health   1890,  Purification  of  Sewage 
and  Water,  page  747. 

\  Water  Purification  at  Cincinnati,  p.  485. 


THE   COAGULATION  OF   WATERS.  147 

cipitated,  but  this  substance  is  not  entirely  insoluble  in  water 
containing  carbonic  acid.  Under  some  conditions  the  precipitated 
ferrous  hydrate  is  oxidized  by  oxygen  present  in  the  water  to 
ferric  hydrate,  and  so  far  as  this  is  the  case,  good  results  can  be 
obtained.  Ferrous  sulphate  is  not  as  readily  oxidized  when 
applied  to  water  as  is  the  ferric  carbonate  present  in  many  natural 
waters,  and  for  this  reason  ferrous  sulphate  has  not  been  success- 
fully used  in  water  purification.  In  the  treatment  of  sewage, 
where  the  requirements  are  somewhat  different,  it  has  been  one 
of  the  most  satisfactory  coagulants. 

Ferric  sulphate  acts  in  much  the  same  way  as  sulphate  of 
alumina,  and  is  entirely  suitable  for  use  where  sulphate  of  alumina 
could  be  employed,  but  it  has  not  been  used  in  practice,  due  prob- 
ably to  its  increased  cost  as  compared  with  its  effect,  and  to  the 
practical  difficulties  of  applying  it  in  the  desired  quantities  due 
to  its  physical  condition. 

Metallic  Iron:  The  Anderson  Process. — The  use  of  metallic 
iron  for  water  purification  in  connection  with  a  moderately  slow 
filtration  through  filters  of  the  usual  form  is  known  as  Anderson's 
process  (patented),  and  has  been  used  at  Antwerp  and  elsewhere 
on  a  large  scale,  and  has  been  experimentally  examined  at  a 
number  of  other  places. 

The  process  consists  in  agitating  the  water  in  contact  with 
metallic  iron,  a  portion  of  which  is  taken  into  solution  as  ferrous 
carbonate.  Upon  subsequent  aeration  this  is  supposed  to  become 
oxidized  and  precipitate  out  as  ferric  hydrate, 'with  all  the  good 
and  none  of  the  bad  effects  which  follow  the  use  of  alum.  The 
precipitate  is  partially  removed  by  sedimentation,  while  filtration 
completes  the  process.  The  process  is  admirable  theoretically, 
and  in  an  experimental  way  upon  a  very  small  scale  often  gives 
most  satisfactory  results,  muddy  waters  very  difficult  of  filtration, 
and  colored  peaty  waters  yielding  promptly  clear  and  colorless 
effluents. 

In  applying  the  process  on  a  larger  scale,  however,  with  peaty 


148  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

waters  at  least,  it  seems  impossible  to  get  enough  iron  to  go  into 
solution  in  the  time  which  can  be  allowed,  and  the  small  quantity 
which  is  taken  up  either  remains  in  solution  or  else  slowly  and 
incompletely  precipitates  out,  without  the  good  effects  which 
follow  the  sudden  and  complete  precipitation  of  a  larger  quantity, 
and  in  this  case  the  color  is  seldom  reduced,  and  may  even  be 
increased  above  the  color  of  the  raw  water  by  the  iron  remaining 
in  solution. 

The  ingenuity  of  those  who  have  studied  the  process  has  not 
yet  found  any  adequate  means  of  avoiding  these  important  prac- 
tical objections;  and  even  at  Antwerp  a  great  extension  of  the 
filtering  area,  as  well  as  the  use  of  alum  at  times  of  unusual  pollu- 
tion, is  good  evidence  that  simple  filtration,  in  distinction  from 
the  effect  of  the  iron,  is  relied  upon  much  more  than  formerly. 

At  Dordrecht  also,  where  the  process  has  been  long  in  use, 
the  rate  of  filtration  does  not  exceed  the  ordinary  limits;  nor  is 
the  result,  so  far  as  I  could  ascertain,  in  any  way  superior  to  that 
obtained  a  few  miles  away  at  Rotterdam,  by  ordinary  filtration, 
with  substantially  the  same  raw  water. 

The  results  obtained  at  Boulogne-sur-Seine,  near  Paris,  have 
been  closely  watched  by  the  public  chemist  and  bacteriologist  of 
Paris,  and  have  been  very  favorable,  and  a  number  of  new  plants 
of  very  considerable  capacity  have  been  built,  to  supply  some  of 
the  suburbs  of  Paris,  but  even  in  these  cases  only  moderate  rates 
of  filtration  are  employed  which  would  yield  excellent  effluents 
without  the  iron. 

Compounds  of  Manganese. — Manganese  forms  compounds  simi- 
lar to  those  of  iron,  that  is  to  say  manganous  and  manganic  salts, 
but  their  use  in  connection  with  water  filtration  has  not  been 
found  possible.  In  addition,  manganese  forms  a  series  of  com- 
pounds, known  as  manganates  and  permanganates,  quite  different 
in  their  structure  and  action  from  the  others.  These  compounds 
contain  an  excess  of  oxygen  which  they  give  up  very  readily  to 
organic  matters  capable  of  absorbing  oxygen,  and  because  of  this 


THE    COAGULATION  OF   WATERS.  149 

power,  they  have  been  extensively  used  in  the  treatment  of 
sewage.  Applied  to  the  treatment  of  waters  their  action  is  very 
slight,  and  the  compounds  are  so  expensive  that  they  have  not 
been  employed  for  this  purpose.  Theoretically  the  action  is  very 
attractive,  as  the  oxygen  liberated  by  their  decomposition  oxidizes 
some  of  the  organic  matter  of  the  water,  thereby  purifying  it  in 
part,  while  the  manganese  is  precipitated  as  a  flocculent  precipi- 
tate having  all  of  the  advantages  pertaining  to  a  precipitate  of 
hydrate  of  alumina,  and  without  the  disadvantage  of  adding  acid 
to  the  water,  as  is  the  case  with  the  compounds  of  alumina  and 
iron.  These  chemicals,  when  used  in  comparatively  concentrated 
condition,  have  powerful  germicidal  actions,  but  in  water  purifica- 
tion the  amounts  which  can  be  used  are  so  small  that  no  action  of 
this  kind  results.  The  amount  which  can  be  applied  to  a  water  is 
limited  to  the  amount  which  can  be  decomposed  by  the  organic 
matters  present  in  the  water,  and  is  not  large. 

The  Use  of  Metallic  Iron  and  Aluminum,  with  the  Aid  of 
Electricity. — Elaborate  experiments  were  made  at  Louisville  with 
metallic  iron  and  aluminum  oxidized  and  made  available  by  the 
aid  of  electric  currents.  The  use  of  iron  with  electric  currents  was 
tried  in  sewage  purification  some  years  ago,  under  the  name  of  the 
Webster  process,  but  wasYiever  put  to  practical  use.  The  theory 
is  to  oxidize  the  iron  or  aluminum  in  contact  with  the  water,  with 
the  formation  of  flocculent  hydrates,  by  the  aid  of  an  electric 
current,  thereby  securing  the  advantages  of  the  application  of 
salts  of  these  metals  to  the  water  without  the  disadvantage  of  the 
addition  of  acid. 

Other  Chemicals  Employed. — A  solution  containing  chlorine 
produced  by  electrical  action  has  been  suggested.  Chlorine  is 
a  powerful  disinfectant,  and  when  used  in  large  quantities  kills 
bacteria.  It  is  not  possible  to  use  enough  chlorine  to  kill  the 
bacteria  in  the  water  without  rendering  it  unfit  for  human  use. 
The  nature  of  this  treatment  has  been  concisely  described  by 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

Dr.  Drown,*  who  shows  that  the  electrically  prepared  fluids  do 
not  differ  in  their  action  in  any  way  from  well-known  chemicals, 
the  use  of  which  would  be  hardly  considered. 

The  use  of  ozone  and  peroxide  of  hydrogen  have  also  been  sug- 
gested, but  I  do  not  know  that  they  have  been  successfully  used 
•  on  a  large  scale.  The  same  is  true  of  many  other  chemicals,  the 
Consideration  of  which  is  hardly  necessary  in  this  connection. 

COAGULANTS    WHICH    HAVE    BEEN    USED. 

In  actual  work  sulphate  of  alumina  is  practically  the  only 
coagulant  which  has  been  employed,  excepting  the  alums,  which 
are  practically  its  equivalent  in  action,  differing  only  in  strength. 
Nearly  all  important  experiments  upon  the  coagulation  of  water 
have  been  made  with  sulphate  of  alumina,  and  in  the  further  dis- 
cussion of  this  subject  only  this  coagulant  will  be  considered. 

AMOUNT    OF    COAGULANT    REQUIRED    TO    REMOVE   TURBIDITY. 

In  the  coagulation  of  turbid  waters  a  certain  definite  amount 
of  coagulant  must  be  employed.  If  less  than  this  amount  is  used 
either  no  precipitate  will  be  formed,  or  it  will  not  be  formed  in 
sufficient  bulk  to  effect  the  desired  results.  It  is  necessary  that 
the  precipitate  should  be  sufficient,  and  that  it  should  be  formed 
practically  all  at  one  time.  The  amount  of  coagulant  necessary 
to  accomplish  this  purpose  is  dependent  upon  the  turbidity  of  the 
raw  water.  With  practically  clear  waters  sulphate  of  alumina  of 
the  ordinary  commercial  strength,  that  is  to  say,  with  about  17 
per  cent  soluble  oxide  of  aluminum,  used  in  quantities  as  small  as 
0.3  or  0.4  of  a  grain  per  gallon,  will  produce  coagulation.  As  the 
turbidity  increases  larger  amounts  must  be  employed. 

A  special  study  was  made  of  this  point  in  connection  with  the 
Pittsburg  experiments. f  As  an  average  of  these  results  it  was 
found  that  two  grains  per  gallon  of  sulphate  of  alumina  were 

*  Jour,  of  the  New  England  Water  Works  Assoc.,  Vol.  vm,  page  183. 
f  Report  of  the  Pittsburg  Filtration  Commission,  1899,  page  55. 


THE    COAGULATION   OF   WATERS. 


required  to  properly  coagulate  waters  having  turbidities  of  i.oo,  so 
that  they  could  be  filtered  by  the  Jewell  filter,  and  2.75  grains 
were  required  for  the  Warren  filter. 

Aside  from  the  amount  required  to  produce  a  precipitate  in 
the  clearest  waters,  the  amount  of  coagulant  required  was  pro- 
portional to  the  turbidity.  As  an  average  for  the  two  filters  the 


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VND  THE  AMOUNTS  NECESS/ 
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Turbidity  of  Raw  W<rTer 

FIG.  20. — AMOUNT  OF  COAGULENT  REQUIRED  TO  REMOVE  TURBIDITY. 

required  quantity  was  approximately  0.30  of  a  grain,  and  in 
addition  0.02  of  a  grain  for  each  o.oi  of  turbidity.  Thus  a  water 
having  a  turbidity  of  0.20  requires  0.70  of  a  grain  per  gallon ;  a 
water  having  a  turbidity  of  0.50  requires  1.30  grains;  of  i.oo, 
2.30  grains;  of  2.00,  4.30  grains,  etc.  These  are  average  minimum 
results.  Occasionally  clear  effluents  were  produced  with  smaller 
quantities  of  coagulant,  while  at  other  times  larger  quantities  were 
necessary  for  satisfactory  results. 


152 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


The  amount  of  coagulant  required  for  clarification  at  Cincinnati 
has  been  stated  by  Mr.  Fuller  in  his  report.  A  number  of  his 
results  are  brought  together  in  the  following  table,  to  which  has 
also  been  added  a  column  showing  approximately  the  correspond- 
ing results  at  Pittsburg. 

ESTIMATED    AVERAGE   AMOUNTS    OF    REQUIRED    CHEMICAL   FOR 
DIFFERENT    GRADES    OF   WATER. 


Chemical  Required 

,  Grains  per  Gallon. 

Suspended  Matter, 
Parts  in  100,000. 

Raw  Water  for 
Sand  Filters. 

Subsided  Water  for 
Sand  Filters. 

Subsided  Water  for 
Mechanical  Filters. 

Minimum  for 
Raw  Water  for 

Cincinnati 

Cincinnati 

Cincinnati 

Mechanical  Filters. 

Report,  Page  290. 

Report,  Page  290. 

Report,  Page  341. 

Pittsburg. 

I.O 

0 

0 

0-75 

0.40 

2-5 

0 

0 

1.25 

0.50 

5-0 

0 

O 

1-50 

0.70 

7-5 

O 

1-30 

i-95 

O.QO 

IO.O 

•50 

1.  60 

2.20 

.OO 

12.5 

.60 

I.  80 

2-45 

•15 

15-0 

.70 

2.00 

2.65 

•30 

17-5 

.80 

2.10 

2.85 

.40 

20..  0 

•95 

2.20 

3-oo 

.60 

30.0 

2.25 

2-45 

3.80 

2.00 

40.0 

2.50 

2-75 

4.40 

2.50 

50.0 

2.80 

6O.O 

3-05 

75-0 

3-40 

100.  0 

4.00 

120.0 

4-75 

Mr.  Fuller's  results  seem  to  show  that  a  greater  amount  of 
coagulant  is  required  for  the  preparation  of  water  for  mechanical 
filters  than  is  necessary  in  connection  with  sand  filters.  The 
results  with  sand  filters  indicate  that  settled  waters  and  raw  waters 
containing  equal  amounts  of  suspended  matters  are  about  equally 
difficult  to  treat.  The  results  at  Pittsburg  indicate  that  the  raw 
waters  required  much  smaller  quantities  of  coagulant  for  given 
amounts  of  suspended  matters  than  was  the  case  with  subsided 
waters  at  Cincinnati,  the  results  agreeing  more  closely  with  the 
amounts  required  to  prepare  raw  water  for  sand  filters  at  Cin- 
cinnati. 


THE   COAGULATION  OF   WATERS.  1 53 

AMOUNT   OF   COAGULANT   REQUIRED   TO    REMOVE   COLOR. 

The  information  upon  this  point  is,  unfortunately,  very  inade- 
quate. In  some  experiments  made  by  Mr.  E.  B.  Weston  at 
Providence  in  1893  with  a  mechanical  filter,*  with  quantities  of 
sulphate  of  alumina  averaging  0.6  or  0.7  of  a  grain  per  gallon,  the 
removal  of  color  was  usually  from  70  to  90  per  cent.  The  stand- 
ard used  for  the  measurement  of  color  is  not  stated,  and  there  is 
no  statement  of  the  basis  of  the  scale,  consequently  no  means  of 
determining  the  absolute  color  of  the  raw  water  upon  standards 
commonly  used. 

At  Westerly,  R.  I.,  with  a  New  York  filter,  the  actual 
quantity  of  potash  alum  employed  from  Oct.  10,  1896,  to  March 
i,  1897,  was  1.94  grains  per  gallon,  the  amount  being  regulated 
to  as  low  a  figure  as  it  was  possible  to  use  to  secure  satisfactory 
decolorization.  There  is  no  record  of  the  color  of  the  raw  water. 
A  very  rough  estimate  would  place  it  at  0.50  upon  the  platinum 
scale.  The  chemical  employed  in  this  case  was  alum,  and  two 
thirds  as  large  a  quantity  of  sulphate  of  alumina  would  probably 
have  done  corresponding  work,  had  suitable  apparatus  for  applying 
it  been  at  hand. 

At  Superior,  Wisconsin,  the  water  in  the  bay  coming  from  the 
St.  Louis  River,  having  a  color  of  2.40  platinum  scale,  was 
treated  experimentally  with  quantities  of  sulphate  of  alumina  up 
to  4  grains  per  gallon,  by  Mr.  R.  S.  Weston  in  January,  1899, 
but  even  this  quantity  of  coagulant  utterly  failed  to  coagulate  and 
decolorize  it. 

At  Greenwich,  Conn.,  during  1898  the  average  amount  of 
sulphate  of  alumina  employed,  as  computed  from  quantities  stated 
in  the  annual  report  of  the  Connecticut  State  Board  of  Health 
for  1898,  was  about  0.44  of  a  grain  per  gallon,  and  this  quantity 
sufficed  to  reduce  the  color  of  the  raw  water  from  0.40  to  0.30, 
platinum  standard.  This  reduction  is  very  slight,  and  it  is 

*  Rhode  Island  State  Board  of  Health  Report  for  1894. 


I$4  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

obvious  that  this  quantity  of  coagulant  was  not  enough  for 
decolorization. 

Some  experiments  bearing  on  color  removal  were  made  at  East 
Providence,  R.  I.,  by  Mr.  E.  B.  Weston,  and  are  described  in 
the  Proceedings  of  the  American  Society  of  Civil  Engineers  for 
September,  1899.  In  this  case  the  color  is  reported  to  have  been 
reduced  from  0.58  to  o.  10  platinum  standard  by  the  use  of  one 
grain  of  sulphate  of  alumina,  containing  22  per  cent  of  effective 
alumina,  equivalent  to  about  1.30  grains  of  the  ordinary  article 
per  gallon. 

The  various  experiments  seem  to  indicate  that  a  removal  from 
80  to  90  per  cent  of  the  color  can  be  effected  by  the  use  of  a 
quantity  of  sulphate  of  alumina  equal  to  rather  more  than  two 
grains  per  gallon  for  waters  having  colors  of  i.oo,  platinum 
standard,  and  proportionate  quantities  for  more  and  less  deeply 
colored  waters.  With  much  less  sulphate  of  alumina  decoloriza- 
tion is  not  effected,  and  even  larger  quantities  do  not  remove  all 
of  the  color. 

The  data  are  much  less  complete  than  could  be  desired,  and 
it  is  to  be  hoped  that  experiments  will  be  undertaken  to  throw 
more  light  upon  this  important  subject. 

SUCCESSIVE   APPLICATION    OF   COAGULANT. 

Mr.  Fuller,  in  his  experiments  at  Louisville,  has  ascertained 
that  when  sulphate  of  alumina  is  added  to  extremely  muddy  water 
the  sediment  absorbs  some  of  the  chemical  before  it  has  time  to 
decompose,  and  carries  it  to  the  bottom,  and  so  far  as  this  is  the 
case,  no  benefit  is  derived  from  that  part  of  the  coagulant  which 
is  absorbed.  In  other  words,  it  is  necessary  to  add  more  coagu- 
lant than  would  otherwise  be  necessary  because  of  this  action. 
The  data  showed  that  different  kinds  of  suspended  matters  took 
up  very  different  amounts  of  coagulant  in  this  way.  With  only 
moderately  turbid  waters  the  loss  of  chemical  from  this  source  is 
unimportant.  Hardly  any  trace  of  it  was  found  at  Pittsburg  with 


THE    COAGULATION  OF    WATERS.  155 

the  Allegheny  River  water.  At  Louisville,  however,  it  was  an 
important  factor,  as  shown  by  Mr.  Fuller's  results. 

To  avoid  this  loss  of  chemical  Mr.  Fuller  has  suggested  the 
removal  of  the  greater  part  of  the  suspended  matters  by  sedimen- 
tation, without  chemicals,  or  with  the  aid  of  a  small  quantity  of 
chemical,  followed  by  the  application  of  the  final  coagulant  prior 
to  filtration.  With  the  worst  waters  encountered  at  Louisville 
the  saving  in  coagulant  to  be  effected  in  this  way  is  very  great. 

Mr.  Fuller  states  in  "  Water  Purification  at  Louisville,'* 
p.  417:  "  The  practical  conclusions  to  be  drawn  from  this  experi- 
ence are  that  with  preliminary  coagulation,  followed  by  subsidence 
for  a  period  of  about  three  hours,  the  application  of  coagulants 
may  be  divided  to  advantage,  and  a  considerable  portion  of  the 
suspended  matter  kept  off  the  filter,  when  the  total  amount  of 
required  coagulant  ranges  from  2  to  2.5  grains  or  more  of  ordinary 
sulphate  of  alumina  per  gallon.  In  the  case  of  a  water  requiring 
more  than  this  amount  of  coagulating  treatment,  a  proper  division 
of  the  application  would  increase  the  saving  of  coagulants  and 
would  diminish  the  frequency  of  washing  the  filter." 

In  his  final  summary  and  conclusions,  page  441,  Mr.  Fuller 
estimates  the  amount  of  sulphate  of  alumina  required  for  the  clari- 
fication of  the  Ohio  River  at  Louisville  at  3.00  grains  per  gallon 
of  water  filtered  if  all  applied  at  one  point,  or  at  1.75  grains  by 
taking  advantage  of  subsidence  to  its  economical  limit  prior  to  the 
final  coagulation.  The  saving  to  be  effected  in  this  way  is  suffi- 
cient to  justify  the  works  necessary  to  allow  it  to  be  carried  out. 
With  less  turbid  waters,  or  waters  highly  turbid  for  only  short 
intervals,  the  advantages  of  double  coagulation  would  be  less 
apparent. 

THE     AMOUNT   OF    COAGULANT    WHICH     VARIOUS     WATERS    WILL 

RECEIVE. 

The  amount  of  coagulant  which  can  be  safely  used  is  dependent 
upon  the  alkalinity  of  the  raw  water.  When  sulphate  of  alumina 


156  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

is  added  to  water  it  is  decomposed,  as  explained  above,  with  the 
formation  of  alumina,  which  is  alone  useful  in  the  work  of  purifica- 
tion, and  sulphuric  acid,  which  combines  with  the  calcium  car- 
bonate or  lime  present  in  the  water.  There  should  always  be  an 
excess  of  alkalinity  or  lime  in  the  raw  water.  If  for  any  reason 
there  is  not,  there  is  nothing  to  combine  with  the  liberated  sul- 
phuric acid,  and  the  decomposition  of  the  coagulant  is  not  com- 
plete, and  a  portion  of  it  goes  undecomposed  into  the  effluent. 
The  effluent  then  has  an  acid  reaction,  and  is  unfit  for  domestic 
supply.  When  distributed  through  iron  pipes,  it  attacks  the  iron, 
rusting  the  pipes,  and  giving  rise  to  all  the  disagreeable  conse- 
quences of  an  iron  containing  water. 

The  amount  of  lime  in  a  water  available  to  combine  with  the 
sulphuric  acid  can  be  determined  by  a  very  simple  chemical  opera- 
tion, namely,  by  titration  with  standard  acid  with  a  suitable  indi- 
cator. The  amount  of  coagulant  corresponding  to  a  given  quantity 
of  lime  can  be  readily  and  accurately  calculated,  but  it  is  not 
regarded  safe  to  use  as  much  sulphate  of  alumina  as  corresponds 
to  the  lime.  The  quantity  of  coagulant  used  is  not  susceptible  to 
exact  control,  but  fluctuates  somewhat,  and  if  the  exact  theoretical 
quantity  should  be  employed  during  24  hours,  there  would  surely 
be  an  excess  during  some  portion  of  that  time  from  which  bad 
results  would  be  experienced.  It  is  therefore  considered  only 
prudent  to  use  three  quarters  as  much  sulphate  of  alumina  as 
corresponds  to  the  lime  in  the  water.  With  sulphate  of  alumina 
containing  17  per  cent  of  soluble  aluminum  oxide  and  the  corre- 
sponding amount  of  sulphuric  acid,  the  amount  which  can  be 
applied  to  a  water  in  grains  per  gallon  is  slightly  less  than  the 
alkalinity  expressed  in  terms  of  parts  in  100,000  of  calcium  car- 
bonate. 

Many  waters  contain  sufficient  lime  to  combine  with  the  acid 
of  all  the  coagulant  which  is  necessary  for  their  coagulation. 
Others  will  not,  and  it  thus  becomes  an  important  matter  to  deter- 
mine whether  a  given  water  is  capable  of  decomposing  sufficient 


THE   COAGULATION  OF   WATERS.  I  57 

coagulant  for  its  treatment.  It  is  usually  the  flood-flows  of  rivers 
which  control  in  this  respect.  The  water  at  such  times  requires 
much  larger  quantities  of  coagulant  for  its  clarification,  and  it  also 
usually  contains  much  less  lime  than  the  low-water  flows.  The 
reason  for  this  is  obviously  that  the  water  of  the  flood-flows  is 
largely  rain-water  which  has  come  over  the  surface  without  coming 
into  very  intimate  contact  with  the  soil,  and  consequently  without 
having  taken  from  it  much  lime,  while  the  low-water  flows  contain 
a  considerable  proportion  of  water  which  has  percolated  through 
the  soil  and  has  thus  become  charged  with  lime. 

In  some  parts  of  the  country,  as,  for  instance,  in  New  England, 
the  soil  and  underlying  rock  are  almost  entirely  free  from  lime, 
and  rivers  from  such  watersheds  are  capable  of  receiving  only  very 
small  quantities  of  coagulant  without  injurious  results. 

The  deficiency  of  alkalinity  in  raw  water  can  be  corrected  by 
the  addition  to  it  of  lime  or  of  soda-ash.  Lime  has  been  used  for 
this  purpose  in  many  cases.  When  used  only  in  moderate  amounts 
it  hardens  the  water,  and  is  thus  seriously  objectionable.  The 
use  of  so  large  a  quantity  as  would  precipitate  out,  as  in  Clark's 
process,  has  not  been  employed  in  practice.  If  it  should  be 
attempted,  the  amount  of  lime  would  require  to  be  very  accurately 
controlled,  and  the  effluent  would  have  to  be  treated  with  carbonic 
acid  to  make  it  suitable  for  supply. 

Waters  so  hard  as  to  require  the  use  of  the  Clark  process  almost 
always  have  sufficient  alkalinity,  and  do  not  require  to  be  treated 
with  lime  in  connection  with  the  use  of  sulphate  of  alumina. 

The  use  of  soda-ash  is  free  from  the  objections  to  the  use  of 
lime,  but  is  more  expensive,  and  would  require  to  be  used  with 
caution.  Its  use  has  often  been  suggested,  but  I  do  not  know 
that  it  has  ever  been  employed  in  practice.  In  small  works  the 
use  of  a  filtering  material  containing  marble-dust,  or  other  cal- 
careous matter,  would  seem  to  have  some  advantages  in  case  of 
deficiency  of  alkalinity,  although  it  would  harden  the  water  so 
treated. 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


The  alkalinities  of  a  number  of  waters  computed  as  parts  in 
100,000  of  calcium  carbonate  (approximately  equal  to  the  safe 
doses  of  sulphate  to  alumina  in  grains  per  gallon)  are  as  follows: 


Maximum. 

Minimum. 

Average. 

Boston  water    1898  «  

2  87 

Oil 

I   08 

Conestoga  Creek>  Lancaster    Penn         

12    2O 

37O 

6  80 

8  oo 

I    O2 

2    QO 

20.  oo 

2    2O 

1O   OO 

Ohio  River    Cincinnati    1898  

7   OO 

2   OO 

4.  CQ 

Ohio  River,  Louisville  

10  87 

2    12 

6  70 

Lake  Erie,  Lorain,  Ohio  

Q    SO 

Lake  Michigan,  Chicago  

II  .  5O 

MECHANICAL   FILTERS.  I  59 


CHAPTER    X. 
MECHANICAL   FILTERS. 

THE  term  mechanical  filters  is  used  to  designate  a  general  class 
of  filters  differing  in  many  respects  quite  radically  from  the  sand 
filters  previously  described.  They  had  their  origin  in  the  United 
States,  and  consisted  originally  of  iron  or  wooden  cylinders  filled 
with  sand  through  which  the  water  was  forced  at  rates  of  one  ta 
two  hundred  million  gallons  per  acre  daily,  or  from  fifty  to  one 
hundred  times  the  rates  usually  employed  with  sand  filters.  These 
filters  were  first  used  in  paper-mills  to  remove  from  the  large 
volumes  of  water  required  the  comparatively  large  particles,  which 
would  otherwise  affect  the  appearance  and  texture  of  the  paper; 
and  in  their  earlier  forms  they  were  entirely  inadequate  to  remove 
the  finer  particles,  such  as  the  bacteria,  and  the  clay  particles 
which  constitute  the  turbidity  of  river  waters.  Various  improve- 
ments in  construction  have  since  been  made,  and,  in  connection 
with  the  use  of  coagulants,  much  more  satisfactory  results  can 
now  be  obtained  with  filters  of  this  class;  and  their  use  has  been 
extended  from  manufacturing  operations  to  municipal  supplies,  in 
many  cases  with  most  satisfactory  results. 

The  information  gathered  in  regard  to  the  conditions  essential 
to  the  successful  design  and  operation  of  these  filters  in  the  last 
few  years  is  very  great,  and  may  be  briefly  reviewed. 

PROVIDENCE    EXPERIMENTS.* 

The  first  data  of  importance  were  secured  from  a  series  of 
experiments  conducted  by  Mr.  Edmund  B.  Weston  of  Providence, 
R.  I.,  in  1893  and  1894,  upon  the  Pawtuxet  river  water  used  by 

*  Report  of  the  Rhode  Island  State  Board  of  Health  for  1894. 


1 60  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

that  city.  The  experimental  filter  was  30  inches  in  diameter,  and 
had  a  layer  of  sand  2  feet  10  inches  deep.  The  sand  was  washed  by 
the  use  of  a  reverse  current,  the  sand  being  stirred  by  a  revolving 
rake  at  the  same  time.  The  amount  of  coagulant  employed  was 
about  0.7  of  a  grain  per  gallon.  The  raw  water  was  practically 
free  from  turbidity,  and  the  filter  was  operated  to  remove  color 
and  bacteria. 

The  removal  of  color,  as  stated  in  Mr.  Weston's  report, 
amounted  to  from  70  to  go  per  cent.  The  experiments  extended 
over  a  period  of  ten  months.  The  rate  of  filtration  employed  was 
about  128  million  gallons  per  acre  daily.  The  bacterial  results  of 
the  first  six  months'  operations  were  rejected  by  Mr.  Weston  on 
account  of  defective  methods  of  manipulation. 

During  the  period  from  November  17,  1893,  to  January  30, 
1894,  the  average  bacterial  efficiency  of  filtration  was  about  95 
per  cent,  and  the  manipulation  was  considered  to  be  in  every 
respect  satisfactory.  The  efficiency  was  occasionally  below  90  per 
cent,  but  for  four  selected  weeks  was  as  high  as  98.6  per  cent. 
The  average  amount  of  sulphate  of  alumina  used,  as  calculated 
from  Mr.  Weston's  tables,  was  two  thirds  of  a  grain  per  gallon. 
The  highest  efficiency  followed  the  application  of  a  solution  of 
caustic  soda  to  the  filtering  material.  The  first  day  following  this 
treatment  the  bacterial  efficiency  was  above  99  per  cent.  After- 
wards it  decreased  until  January  30,  when  the  experiments  were 
stopped.  The  high  bacterial  efficiency  following  the  use  of  caustic 
soda  was  of  such  short  duration  as  to  suggest  very  grave  doubts 
as  to  its  practical  value.  It  is  extremely  unfortunate  that  the 
experiments  stopped  only  a  week  after  this  experiment,  and  the 
results  were  never  repeated.  I  consider  that  the  average  bacterial 
efficiency  of  about  95  per  cent  obtained  for  the  period  of  October 
17  to  January  30,  when  the  manipulation  was  considered  to  be  in 
every  way  satisfactory,  more  nearly  represents  what  can  be  obtained 
under  these  conditions  than  the  results  for  certain  periods,  par- 
ticularly after  the  use  of  the  caustic  soda. 


MECHANICAL   FILTERS.  l6l 

LOUISVILLE    EXPERIMENTS.* 

These  experiments  were  inaugurated  by  the  Louisville  Water 
Company  in  connection  with  the  manufacturers  of  certain  patented 
filters.  Mr.  Charles  Hermany,  Chief  Engineer  of  the  Company, 
had  general  charge  of  the  experiments.  Mr.  George  W.  Fuller 
was  Chief  Chemist  and  Bacteriologist  and  had  direct  charge  of  the 
work  and  has  made  a  most  elaborate  report  upon  the  same.  In 
these  examinations  many  devices  were  investigated ;  but  the  two 
which  particularly  deserve  our  attention  are  the  filters  known  as 
the  Warren  Filter  and  the  Jewell  Filter. 

These  filters  were  operated  for  two  periods,  namely,  from 
October  18,  1895,  to  July  30,  1896,  and  from  April  5  to  July  24, 
1897.  The  investigations  were  directed  toward  the  clarification 
of  the  river  water  from  the  mud,  and  to  the  removal  of  bacteria. 
The  water  was  substantially  free  from  color.  The  character  of  the 
water  at  this  point  was  such  that  in  its  best  condition  at  least 
three  fourths  of  a  grain  of  sulphate  of  alumina  were  necessary  for 
its  coagulation,  and  with  this  and  with  larger  quantities  of  coagu- 
lant fair  bacterial  purification  was  nearly  always  obtained.  The 
problem  studied  therefore  was  principally  that  of  clarification  from 
mud.  The  average  efficiencies,  as  shown  by  the  total  averages, 
(page  248,)  were  as  follows:  Warren  filter,  bacterial  efficiency, 
96.7  per  cent;  Jewell  filter,  96.0  per  cent. 

LORAIN    TESTS.f 

These  tests  were  made  by  the  author  of  a  set  of  Jewell  filters 
at  Lorain,  Ohio.  The  filters  were  six  in  number,  each  17  feet  in 
diameter,  having  an  effective  filtering  area  of  226  square  feet  each, 
or  1356  square  feet  in  all.  The  construction  of  the  filters  was  in 
all  respects  similar  to  the  Jewell  filter  used  at  Louisville.  The 
raw  water  was  from  Lake  Erie,  and  during  the  examination  was 

*  Report  on  the   Investigations  into  the  Purification  of  the  Ohio  River  Water 
at  Louisville,  Kentucky.     D.  Van  Nostrand  &  Co.,  1898. 
f  Ohio  State  Board  of  Health  Report,  1897,  page  154. 


162 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


always  comparatively  clear,  but  contained  considerable  numbers  of 
bacteria.  The  problem  was  thus  entirely  one  of  bacterial  effi- 
ciency. The  question  of  clarification  hardly  presented  itself. 
Although  the  water  became  turbid  at  times  it  did  not  approach  in 
muddiness  the  condition  of  the  Ohio  River  water,  and  an  amount 
of  coagulant  sufficient  for  a  tolerable  bacterial  efficiency  in  all  cases 
was  more  than  sufficient  for  clarification. 

A  summary  of  the  results  obtained  is  as  follows: 


Week  Ending 

6:00  P.M. 

Average  Rate 
of  Filtration, 
Gallons  per 
Sq.  Ft.  Min. 

Sulphate  of 
Alumina, 
Grains  per 
Gallon. 

Bacteria  in 
Lake  Water. 

Bacteria  in 
Effluent. 

Bacterial 
Efficiency 
per  cent. 

06 

2    eg 

16 

26 

IO 

2    CQ 

oQe 

5 

yo.  y 
nfi    A 

Till  v       ^ 

j  j 

2    27 

o°;5 
oA7 

y°  -4 

IO            .... 

28 

I    O7 

JW 

I  54 

y/  •  o 

17    . 

Id. 

180 

26 

yu.  y 

QA     o 

Average   .... 

I.I4 

1.83 

507 

14 

96.4 

The  average  bacterial  efficiency  was  96.4  per  cent  with  1.83  grains 
of  sulphate  of  alumina  per  gallon. 

PITTSBURG    EXPERIMENTS.* 

The  Pittsburg  experiments  were  inaugurated  by  the  Pittsburg 
Filtration  Commission.  The  operation  of  the  filters  extended  from 
January  to  August,  1898.  A  Jewell  and  a  Warren  filter  were 
used  similar  in  design  to  those  used  at  Louisville.  The  raw  water 
contained  large  numbers  of  bacteria,  and  was  also  often  very  turbid, 
although  less  turbid  than  at  Louisville.  At  times  more  coagulant 
was  necessary  for  clarification  than  was  required  for  bacterial  effi- 
ciency; while  as  a  rule  more  was  required  for  satisfactory  bacterial 
purification  than  was  necessary  for  clarification.  The  opportuni- 
ties were  therefore  favorable  for  the  study  of  both  of  these  condi- 
tions. The  amount  of  coagulant  necessary  for  clarification  has 
been  mentioned  in  connection  with  coagulation. 

The    results    secured    upon    the    relation    of    the    quantity   of 

*  Report  of  the  Pittsburg  Filtration  Commission,  City  Document,  1899. 


MECHANICAL   FILTERS.  1 6$ 

coagulant  to  the  number  of  bacteria  in  the  effluent  were  more 
complete  than  any  other  experiments  available,  and  are  therefore 
here  reproduced  from  the  Pittsburg  report  nearly  in  full. 

It  was  found  that  the  amount  of  sulphate  of  alumina  employed 
was  more  important  than  any  other  factor  in  determining  the 
bacterial  efficiency,  and  special  experiments  were  made  to  estab- 
lish the  effect  of  more  and  of  less  coagulant  than  used  in  the 
ordinary  work.  These  experiments  were  made  upon  the  Warren 
filter  during  May,  and  with  the  Jewell  filter  during  June.  The 
monthly  averages  for  these  months  are  thus  abnormal  and  are  not 
to  be  considered.  The  remaining  six  months  for  each  filter  may 
be  taken  as  normal  and  as  representing  approximately  the  work  of 
these  filters  under  ordinary  careful  working  conditions. 

During  the  six  months  when  the  Warren  filter  was  in  normal 
order  the  raw  water  contained  11,531  bacteria  and  the  effluent 
20 1,  the  average  bacterial  efficiency  being  98.26  per  cent.  The 
bacterial  efficiency  was  very  constant,  ranging  only,  by  months,, 
from  97.48  to  98.96  per  cent.  During  the  same  period  a  sand 
filter  receiving  the  same  water  yielded  an  effluent  having  an 
average  of  105  bacteria  per  cubic  centimeter. 

The  Jewell  filter,  for  the  six  months  in  which  it  was  in  normal 
order,  received  raw  water  containing  an  average  of  11,481  bacteria 
and  yielded  an  effluent  containing  an  average  of  293,  the  bacterial 
efficiency  being  97.45  per  cent,  and  ranging,  in  different  months, 
from  93.23  to  98.61  per  cent. 

WASTING    EFFLUENT   AFTER   WASHING   FILTERS. 

After  washing  a  mechanical  filter  the  effluent  for  the  first  few 
minutes  is  often  inferior  in  quality  to  that  obtained  at  other  times, 
and  if  samples  are  taken  at  these  times  and  averaged  with  other 
samples  taken  during  the  run,  an  apparent  efficiency  may  be 
obtained  inferior  to  the  true  efficiency.  To  guard  against  this 
source  of  error,  whenever  samples  have  been  taken  at  such  times, 
the  average  work  for  the  day  has  been  taken,  not  as  the  numerical 


164 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


average  of  the  results,  but  each  sample  has  been  given  weight  in 
proportion  to  the  amount  of  time  which  it  could  be  taken  as 
representing;  so  that  the  results  represent  as  nearly  as  possible 
the  average  number  of  bacteria  in  the  effluent  for  the  whole  run. 
.As  a  matter  of  fact,  however,  comparatively  few  samples  were 
taken  during  these  periods  of  reduced  efficiency,  and  thus  most  of 
the  results  represent  the  normal  efficiency  exclusive  of  this  period. 
A  study  has  been  made,  however,  of  the  results  of  examinations 
of  samples  taken. directly  after  washing,  somewhat  in  detail.  The 
following  is  a  tabular  statement  of  the  average  results  obtained 
from  each  filter  by  months,  including  only  the  results  obtained  on 
those  days  when  samples  were  taken  within  twenty  minutes  after 
washing,  the  results  of  other  days  being  excluded. 

AVERAGE  NUMBER  OF  BACTERIA  IN  EFFLUENT. 


Shown  by 
Record  Sheets. 

Within  Ten 
Minutes  after 
Washing. 

II    tO  20 

Minutes  after 
Washing. 

More  than 
Twenty 
Minutes  after 
Washing. 

WARREN    FILTER. 

1  1  c 

118 

1  14 

March  

•u6 

5° 

cjc 

3OI 

70 

41  7 

207 

75 

May 

(Special 

experiments 

,  omitted  ) 

IQ7 

4Q7 

272 

1  70 

July 

qOO 

S46 

207 

^6 

60  1 

221 

JEWELL    FILTER. 

OJCT 

2.12^ 

2OQQ 

March 

AC  C 

6C7 

QCg 

TCI 

QQ 

66  «; 

462 

165 

May 

J44 

QOS 

146 

127 

(Special 

experiments 

omitted.) 

Tulv 

27Q 

I33O 

272 

274 

•544 

612 

323 

376 

The  time  of  inferior  work  very  rarely  exceeded  twenty  minutes. 
It  will  be  seen  from  the  tables  that  the  results  as  shown  by  the 
record  sheets  are  never  very  much  higher,  and  are  occasionally 
lower  than  the  results  of  samples  taken  on  corresponding  days 
more  than  twenty  minutes  after  washing;  and  thus  while  a 
decrease  in  bacterial  efficiency  was  noted  after  washing,  no 


MECHANICAL   FILTERS.  165 

material  increase  in  the  average  bacterial  efficiency  of  the  mechani- 
cal filters  would  have  been  obtained  if  these  results  had  been 
excluded.  The  results  for  the  whole  time  would  be  affected  much 
less  than  is  indicated  by  the  table,  because  the  table  includes  only 
results  of  those  days  when  samples  were  taken  just  after  washing, 
while  the  much  larger  number  of  days  when  no  such  samples  were 
taken  would  show  no  change  whatever. 

It  has  been  suggested  that  these  inferior  effluents  after  washing 
should  be  wasted.  Such  a  procedure  would  mean  wasting  prob- 
ably on  an  average  two  per  cent  of  the  water  filtered,  and  a  corre- 
sponding increase  in  the  cost  of  filtering.  Mr.  Fuller*  in  his 
Louisville  report  comes  to  the  conclusion  that  with  adequate 
washing  and  coagulation  it  is  unnecessary  to  waste  any  effluent, 
and  that  inferior  results  after  washing  usually  indicate  incomplete 
washing.  While  our  experiments  certainly  indicate  a  reduction  in 
efficiency  after  washing  so  regular  and  persistent  as  to  make  it 
doubtful  whether  incomplete  washing  can  be  the  cause  of  it,  it 
may  be  questioned  whether  or  not  wasting  the  effluent  would  be 
necessary  or  desirable  in  actual  operation.  At  any  rate  the  results 
as  given  in  this  report  are  not  materially  influenced  by  this  factor. 

INFLUENCE  OF  AMOUNT  OF  SULPHATE  OF  ALUMINA  ON  BAC- 
TERIAL EFFICIENCY  OF  MECHANICAL  FILTERS. 
The  number  of  bacteria  passing  a  mechanical  filter  is  dependent 
principally  upon  the  amount  of  sulphate  of  alumina  used;  and  by 
using  a  larger  quantity  of  sulphate  of  alumina  than  was  actually- 
used  in  the  experiments  the  bacterial  efficiency  could  be  consider- 
ably increased.  To  investigate  this  point,  the  results  obtained 
each  day  with  each  of  the  mechanical  filters  were  arranged  in  the 
order  of  the  sulphate  of  alumina  quantities  used,  and  averaged  by 
classes.  In  this  and  the  following  tables  a  few  abnormal  results 
were  omitted. f  A  summary  of  the  results  is  as  follows: 

*  Fuller,  Water  Purification  at  Louisville,  page  425. 

f  Warren,  Feb.  9;  June  i;  July  6.     Jewell,  July  i;  Feb.  9,  16.  17. 


166 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


SUMMARY    OF    RESULTS    WITH    WARREN    MECHANICAL    FILTER, 
ARRANGED   ACCORDING   TO    SULPHATE    OF   ALUMINA    QUANTITIES. 


Number 
of  Days 
Represented. 

Turbidity. 

•  Bacteria. 

Per  cent 
remaining. 

Per  cent 
removed. 

Sulphate  of 
Alumina 
used  Grains 
per  Gallon. 

Raw  Water. 

Effluent. 

7 

0.05 

4,773 

1713 

35.89 

64.11 

o.oo 

2 

0.08 

2,785 

850 

30.52 

69.48 

0.12 

4 

O.  IO 

5)109 

726 

14.21 

85.79 

0.26 

2 

O.2O 

8,713 

214 

2-45       ,       97-55 

0.36 

8 

O.O6 

3,224 

112 

3-47 

96.53 

o-44 

19 

0.06 

3,488 

123 

3-53 

96.47 

0-55 

ii 

0.06 

5,673 

154 

2.71 

97.29 

0.64 

10 

0.10 

6,100 

112 

1.84 

98.16 

0-74 

8 

O.Og 

8,647 

148 

i.7i 

98.29 

0.85 

5 

o.  16 

5,645 

142 

2.52 

97.48 

0-93 

13 

O.I2 

10,397 

2OO 

1.92 

98.08 

.07 

10 

0.08 

12,778 

121 

0-95 

99-05 

•13 

13 

o.  14 

13,397 

I64 

1.22 

98.78 

•25 

iQ 

0.13 

10,462 

1  6O 

i-53 

98.47 

•34 

10 

0.12 

12,851 

107 

0.83 

99.17 

.46 

4 

0.27 

16,015 

77 

0.48 

99-52 

•57 

7 

0-53 

12,262 

191 

1.18 

98.82 

.64 

4 

0.58 

26,950 

347 

1.29 

98.71 

•74 

5 

0.29 

14,570 

86 

0-59 

99.41 

.84 

3 

0.23 

13,833 

153 

I,  II 

98.89 

.92 

19 

0.40 

18,222 

92 

o.  50 

99-50 

2.48 

5 

0-45 

29,300 

1119 

3.82       1       96.18 

3-37 

5 

i.  06 

33,030 

535 

1.62 

98.38 

8.06 

SUMMARY    OF    RESULTS    WITH    JEWELL    MECHANICAL    FILTER, 
ARRANGED    ACCORDING    TO    SULPHATE    OF   ALUMINA    QUANTITIES. 


Number 
of  Days 
'Represented. 

Turbidity. 

Bacteria. 

Per  cent 
remaining. 

Per  cent 
removed. 

Sulphate  of 
Alumina 
used  Grains 
per  Gallon. 

Raw  Water. 

Effluent. 

6 

0.03 

14,037 

6217 

44.29 

55-71 

O.OO 

5 

0.07 

4,267 

680 

15-93 

84.07 

O.24 

14 

O.o6 

2,613 

170 

6.50 

93.50 

0-35 

IO 

0.06 

2,446 

U3 

4.62 

95.38 

0-44 

9 

O.II 

7,303 

234 

3-20 

96.80 

0.55 

20 

0.09 

6,979 

2  2O 

3-15 

96.85 

0.65 

9 

0.08 

5,i9i 

130 

2.50 

97.50 

0.75 

16 

0.12 

8,504 

242 

2.84 

97.16 

0.83 

22 

0.16 

8,506 

99 

1.16 

98.84 

0.96 

12 

O.II 

11,998 

246 

2.05 

97-95 

1.05 

14 

0.18 

18,982 

423 

2.23 

97-77 

.16 

5 

0.14 

13,981 

224 

i.  60 

98.40 

•23 

9 

0.27 

19,806 

325 

1.64 

98-36 

•34 

14 

0.27 

16,549 

324 

1.96 

98.04 

•45 

9 

0.29 

12,194 

96 

0.79 

99.21 

•54 

6 

0.25 

13,483 

5i 

0.38 

99.62 

•65 

7 

0-53 

24,243 

220 

0.91 

99.09 

.72 

3 

0.90 

20,953 

602 

2.88 

97.12 

.90 

5 

0-43 

25,958 

307 

1.19 

98.81 

2.19 

4 

0.84 

21,017 

228 

1.09 

98.91 

3-7i 

MECHANICAL   FILTERS. 
These  results  are  shown  graphically  by  Fig.  21 


167 


L 

o  / 

M 

_, 

- 

99. 
97. 

95. 

99 

'^^ 

V 

1 

V 

I 

J 

j^j 

—  ^ 

II  Fjjtfr_  

/ 

'"\ 

•« 

=- 

/f 

N 

\ 

\  I 

/ 

\ 

\  i 

^ 

r 

\j 

0 

/ 

CITY  OF  PITTSBURGH 
riLTRATION    COMMISSION 

95 

: 

BAG* 

MET 

FERIAL  EFFICIENCIES  OF 
;HANICAL  FILTERS  WITH 

iRlOUS  QUANTITIES  OF 
SULPHATE  OF  ALUMINA 

r 

Waaxa.fih 

V/ 
€ 

^i.p. 

0 

: 

i   i   t    i 

1111 

Dec.  /ff»0.      - 

0                          05                           10                            15                           2.O                          25                          JO                         J. 

Sulphcrte  of  Alumina  used  in  grains  per  gallon. 

FIG.  21. — BACTERIAL  EFFICIENCIES  OF  MECHANICAL  FILTERS. 


INFLUENCE     OF   DEGREE    OF    TURBIDITY    UPON     BACTERIAL   EFFI- 
CIENCY   OF    MECHANICAL    FILTERS. 

It  will  be  noticed  by  referring  to  the  tables  that  as  the  sulphate 
of  alumina  quantities  increased  the  turbidities  increased  and  the 
numbers  of  bacteria  increased,  as  well  as  the  bacterial  efficiencies. 
That  is  to  say,  with  the  less  turbid  waters,  small  sulphate  of 
alumina  quantities  have  been  used,  the  numbers  of  bacteria  in  the 
raw  water  have  been  low,  and  the  bacterial  efficiencies  have  also 
been  low.  With  turbid  waters  much  larger  quantities  of  sulphate 
of  alumina  have  been  used,  the  raw  water  has  contained  more 
bacteria,  and  the  bacterial  efficiencies  have  been  higher.  It  may 


1 68 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


be  then  that  the  increased  efficiencies  with  increased  quantities  of 
sulphate  of  alumina  are  not  due  alone  to  the  increased  sulphate  of 
alumina,  but  in  part  also  to  other  conditions.  Thus -it  may  be 
easier  to  remove  a  large  percentage  of  bacteria  from  a  water  con- 
taining many  than  from  a  water  containing  only  a  few. 

To  investigate  this  matter  and  eliminate  the  influence  of 
turbidity  and  numbers  of  bacteria  in  the  raw  water,  the  results 
were  first  classified  with  reference  to  turbidity.  The  results  with, 
waters  having  turbidities  of  o.  10  or  less,  and  called  for  convenience 
turbid  waters,  are  arranged  by  alum  quantities  as  before.  After- 
wards the  results  obtained  with  turbidities  from  o.  1 1  to  0.50,  and 
called  for  convenience  muddy  waters,  are  grouped;  and  finally  the 
results  with  turbid  water  having  turbidities  of  0.51  and  over,  and 
called  for  convenience  thick  waters.  The  results  thus  arranged 
are  as  follows: 


SUMMARY  OF  RESULTS  WITH  WARREN  MECHANICAL  FILTER, 
ARRANGED  ACCORDING  TO  TURBIDITIES  AND  SULPHATE  OF 
ALUMINA  QUANTITIES. 


Number 
of  Days 
Represented. 

Turbidity. 

Bacteria. 

Per  cent 
remaining. 

Per  cent 
removed. 

Sulphate  of 
Alumina 
used  Grains 
per  Gallon. 

Raw  Water. 

Effluent. 

7 

0.05 

4,773 

1713 

35.89 

64.  II 

o.oo 

2 

0.07 

2,785 

850 

30.52 

69.48 

O.  12 

12 

O.O6 

3,209 

224 

7.00 

93-oo 

0.42 

31 

O.O6 

4.238 

119 

2.8l 

97.19 

0.60 

9 

O.O6 

7,953 

130 

1.64 

98.36 

0.84 

16 

0.04 

11,265 

137 

1.22 

98.78 

I.  II 

29 

0.06 

11,500 

158 

i-37 

98.63 

1.58 

5 

0.17 

8,783 

416 

4-73 

95-27 

0.36 

10 

o.  16 

6,535 

I65 

2-54 

97.46 

0.85 

13 

o.  19 

13,253 

1  86 

1.40 

98.60 

I.I3 

15 

0.22 

10,944 

93 

0.85 

99.15 

1.36 

13 

0.29 

14,089 

112 

0.80 

99.20 

i-73 

10 

o-35 

18,088 

102 

0-57 

99-43 

2.38 

5 

0.29 

25,58o 

540 

2.  II 

97.89 

4-30 

6 

0.87 

25,433 

369 

1-45 

98.55 

1.74 

6 

0-73 

26,566 

79 

0.30 

99.70 

2.64 

4 

1-35 

42,037 

1388 

3-30 

96.70 

8.16 

MECHANICAL   FILTERS. 


[69 


SUMMARY  OF  RESULTS  WITH  JEWELL  MECHANICAL  FILTER, 
ARRANGED  ACCORDING  TO  TURBIDITIES  AND  SULPHATE  OF 
ALUMINA  QUANTITIES. 


Number 
of  Days 
Represented. 

Turbidity. 

Bacteria. 

Percent 
remaining. 

Per  cent 
removed. 

Sulphate  of 
Alumina 
used  Grains 
per  Gallon. 

Raw  Water. 

Effluent. 

6 

0.03 

14,037 

6217 

44.29 

55-71 

0.00 

3 

0.07 

5,170 

991 

19.15 

80.85 

O.  21 

25 

0.05 

2,403 

143 

5-95 

94.05 

0.38 

2O 

O.O6 

6,53' 

I85 

2.84 

97.16 

0.64 

27 

0.06 

5,8n 

122 

2.  IO 

97.90 

0.88 

14 

0.06 

14,978 

412 

2.75 

97.25 

i.  ii 

10 

0.06 

15,787 

390 

2.47 

97-53 

i-37 

10 

0.05 

10,847 

47 

0-43 

99-57 

2.17 

14 

o.  16 

7,525 

256 

3-40 

96.60 

0.60 

17 

0.24 

11,310 

208 

1.84 

98.16 

0.91 

15 

0.24 

15,441 

262 

1.70 

98-30 

1.13 

10 

0.28 

17,842 

232 

1.30 

98.70 

1-43 

8 

0.29 

9,556 

59 

O.62 

99.38 

1-59 

4 

0.29 

20,212 

135 

0.67 

99-33 

2.00 

5 

0.66 

23,680 

336 

1.42 

98.58 

1.42 

7 

0.96 

30,200 

475 

i-57 

98.43 

i-74 

4 

1-25 

37,587 

496 

1.32 

98.68 

2.81 

The  following  table  shows  the  bacterial  efficiencies  with  turbid, 
muddy,  and  thick  waters,  with  substantially  equal  quantities  of 
sulphate  of  alumina: 


Grains  of  Sulphate  of  Alumina. 


Corresponding  Bacterial  Efficiencies. 


Turbid. 

Muddy. 

Thick. 

Turbid. 

Muddy. 

Thick. 

0.42 
0.84 
I.  II 

I.58 

0.36 
0.85 
I-I3 
1-73 
2.38 
4.30 

0.60 
0.91 
I-I3 
1-43 
1.59 

2.00 

WARRE 

N    FILTER. 

93-oo 

98-36 
98.78 
98.63 

95-27 
97.46 
98.60 
99.20 

99-43 
97.89 

96.60 
98.16 
98.30 
98.70 
99-38 
99-33 

1.74 
2.64 
8.16 

JEWEL 

98.55 
99.70 
96.70 

0.64 

0.88 
i.  ii 

1-37 
2.17 

L   FILTER. 
97.16 
97.90 
97.25 
97-53 

99-57 

1.42 

1.74 
2.8l 

98.58 
98.43 
98.68 

170  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

It  appears  from  this  table  that  waters  of  various  degrees  of 
turbidity  give  substantially  equal  bacterial  efficiencies  with  equal 
quantities  of  sulphate  of  alumina,  the  results  varying  as  often  in 
one  direction  as  the  other.  Within  certain  limits  it  may  thus  be 
said  that  turbidity  is  without  influence  upon  the  bacterial  efficiency 
obtained  in  mechanical  nitration. 

It  must  be  borne  in  mind,  however,  that  the  quantities  of 
sulphate  of  alumina,  with  very  few  exceptions,  were  sufficient  to 
produce  full  coagulation.  Mr.  Fuller  has  shown  in  his  Louisville 
report  that  considerable  quantities  of  sulphate  of  alumina  may  be 
added  to  turbid  waters  without  producing  appreciable  coagula- 
tion; and  therefore  if  a  quantity  of  sulphate  of  alumina  sufficient 
to  produce  a  certain  bacterial  efficiency  in  a  clear  water  should  be 
added  to  a  water  so  turbid  that  it  was  unable  to  coagulate  it, 
scarcely  any  effect  would  be  produced.  The  above  statement 
therefore  only  applies  in  those  cases  where  sufficient  sulphate  of 
alumina  is  used  to  adequately  coagulate  the  water. 

As  the  numbers  of  bacteria  often  vary  with  the  turbidity,  the 
variation  in  the  numbers  of  bacteria  in  the  different  classes  is  much 
less  than  in  the  first  tables;  but  to  further  investigate  the  question 
of  whether  the  numbers  of  bacteria  in  the  raw  water  have  an 
important  influence  upon  the  bacterial  efficiencies,  each  of  the  two 
largest  classes  in  the  foregoing  tables  was  divided  into  two  parts, 
according  to  the  bacterial  numbers  in  the  raw  water,  namely,  the 
results  from  the  Jewell  filter  with  turbid  waters  and  with  sulphate 
of  alumina  quantities  ranging  from  0.75  to  i.oo  grain  per  gallon, 
and  the  results  from  the  Warren  filter  with  turbid  waters  and 
with  sulphate  of  alumina  quantities  of  1.25  grains  per  gallon  and 
upward.  The  results  are  as  follows: 


MECHANICAL   FILTERS. 


171 


Number 
of  Days 
Represented. 

Turbidity. 

Bacteria. 

Per  cent 
remaining. 

Per  cent 
removed. 

Sulphate  of 
Alumina 
used  Grains 
per  Gallon. 

Raw  Water. 

Effluent. 

JEWELL    FILTER. 

0-05          I  3.938       I  Si  2.06 

0.07  7,827  167  2.13 

WARREN   FILTER. 


97-94 
97.87 


0.88 
0.87 


15 

14 

0.06 
0.06 

3,545 

20,022 

59 
265 

1.66 
1.32 

98.34 
98.68 

1.67 
1.48 

It  will  be  observed  that  the  bacterial  efficiencies  are  substan- 
tially the  same,  with  the  lower  and  with  the  higher  numbers  of 
bacteria  in  the  raw  water.  That  is  to  say,  other  things  being 
equal,  as  the  number  of  bacteria  increase  in  the  raw  water  the 
number  of  bacteria  in  the  effluent  increase  in  the  same  ratio.  A 
further  analysis  of  other  groups  of  results  would  perhaps  show 
variations  in  one  direction  or  the  other,  but  on  the  whole  it  is 
believed  that  the  comparison  is  a  fair  one,  and  that  there  is  no 
well-marked  tendency  for  bacterial  efficiencies  of  mechanical  filters 
to  increase  or  decrease  with  increasing  numbers  of  bacteria. 


AVERAGE  RESULTS  OBTAINED  WITH  VARIOUS  QUANTITIES  OF 
SULPHATE  OF  ALUMINA. 

As  it  appears  that  neither  the  turbidity  nor  the  number  of 
bacteria  in  the  raw  water  has  a  material  influence  upon  the  per- 
centage bacterial  efficiency  obtained,  we  can  take  the  results  given 
above,  which  include  all  the  results  obtained  (except  a  very  few 
abnormal  ones)  for  computing  the  various  efficiencies  obtained 
with  various  quantities  of  sulphate  of  alumina.  These  results  are 
graphically  shown  by  Fig.  21,  p.  167,  on  which  lines  have  been 
drawn  indicating  the  normal  efficiencies  from  various  quantities 
of  sulphate  of  alumina  as  deduced  from  our  experiments. 

In  computing  the  amount  of  sulphate  of  alumina  which  it 
would  be  necessary  to  use  in  operating  a  plant  at  a  given  place  to 


172  FIL7"RATION   OF  PUBLIC    WATER-SUPPLIES. 

give  these  efficiencies,  the  quantities  of  sulphate  of  alumina  shown 
by  the  diagram  can  be  taken  as  those  which  it  would  be  necessary 
to  use  during  those  days  in  the  year  when  the  raw  water  was  clear, 
or  sufficiently  clear,  so  that  the  amounts  of  sulphate  of  alumina 
mentioned  would  suffice  to  properly  coagulate  it. 


TYPES    OF    MECHANICAL    FILTERS. 

Sections  of  the  Warren  and  Jewell  filters  used  at  Pittsburg  are 
presented  herewith.  The  filters  here  shown  are  practically  identi- 
cal with  those  used  at  Lorain  and  Louisville,  and  nearly  all  the 
exact  information  regarding  mechanical  filters  relates  to  filters  of 
these  types.  These  sections  show  clearly  the  constructions  used  at 
Pittsburg  and  Louisville,  but  there  are  some  points  in  connection 
with  the  designs  of  these  filters  which  require  to  be  considered  more 
in  detail. 

The  simplest  idea  of  a  mechanical  filter  is  a  tub,  with  sand  in 
the  bottom  and  some  form  of  drainage  system.  Water  is  run  over 
the  sand,  passes  through  it,  and  is  collected  by  the  drainage 
system.  When  the  sand  becomes  clogged  it  is  washed  by  the  use 
of  a  reverse  current  of  water.  This  reverse  current  of  water  is  so 
rapid  as  to  preclude  the  use  of  a  drainage  system  consisting  of 
gravel,  tile-drains,  etc.,  such  as  are  used  in  sand  filters  operated 
at  lower  rates,  and  instead  metallic  strainers  in  some  form  are 
used.  The  sand  comes  directly  against  these  strainers,  which  are 
made  as  coarse  as  it  is  possible  to  have  them,  without  allowing 
the  sand  to  pass. 

The  rate  of  washing  is  usually  from  five  to  seven  gallons  per 
square  foot  per  minute.  In  the  Warren  filter  the  openings  in  the 
strainers  at  the  bottom  are  6  to  8  per  cent  of  the  total  area,  and 
during  washing  the  water  has  an  average  velocity  of  0.20  foot  per 
second  upward  through  them.  This  velocity  is  so  slow  that  the 
friction  of  the  water  in  passing  through  the  openings  in  the  screen 
is  practically  nothing.  A  result  of  this  is  that  if  there  is  any 


MECHA  \ICA  L   FIL  TERS. 


173 


unequal  resistance  of  the  sand  to  the  water,  the  bulk  of  the  water 
goes  up  at  the  points  of  least  resistance  in  the  sand. 


FIG.  22. — SECTION  OF  JEWELL  MECHANICAL  FILTER  USED  IN  PITTSBURG 

EXPERIMENTS. 

This  tendency  would  be  fatal  were  it  not  for  the  revolving  rake 
which  loosens  and  mixes  the  sand  and  largely  corrects  it.  The 
correction,  however,  is  imperfect,  and  some  parts  of  the  filter  are 
washed  more  than  others. 

The  rake  is  also  necessary  to  prevent  the  separation  of  sand 
into  coarser  and  finer  particles.  It  is  practically  impossible  to  get 


174  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

filter  sand  the  grains  of  which  are  all  of  the  same  size.  When  a 
filter  is  washed  the  tendency  is  for  the  wash  water  to  go  up  in 
limited  areas.  The  larger  sand  grains  tend  to  collect  at  these 
points  while  the  finer  grains  collect  in  places  where  there  is  no 
upward  current,  or  where  it  is  less  rapid.  In  many  filters  this 
tendency  is  very  strong.  The  revolving  rake  is  necessary  to  cor- 
rect it,  and  to  keep  the  sand  thoroughly  mixed,  otherwise  when 
a  filter  is  put  in  operation  after  washing,  the  frictional  resistance 
through  the  coarse  sand  being  less,  the  bulk  of  the  water  goes 
through  it,  with  the  result  that  a  part  of  the  area,  and  the  part 
which  is  least  efficient  as  a  filter,  passes  nearly  all  of  the  water, 
and  with  inferior  results. 

In  the  Jewell  filter  provision  is  made  for  the  distribution  of 
the  wash  water  over  the  whole  area  in  another  way.  The  strainers 
have  areas  at  the  surface  amounting  to  1.2  to  1.4  per  cent  of  the 
whole  area,  but  the  water  before  reaching  them  passes  through 
throats  much  smaller  in  size  than  the  strainer  outlets,  and  amount- 
ing in  the  aggregate  to  only  about  0.07  per  cent  of  the  filter  area. 
When  washing  at  a  rate  of  seven  gallons  per  square  foot  per 
minute,  water  passes  through  these  necks  at  a  velocity  of  22  feet 
per  second.  The  friction  and  velocity  head  in  passing  these  necks 
is  estimated  to  be  about  30  vertical  feet,  and  is  so  much  greater 
than  the  friction  of  the  outlets  proper,  and  of  the  sand,  that  the 
water  passes  through  each  strainer  with  approximately  the  same 
velocity,  and  the  wash  water  is  equally  distributed  over  the  whole 
area  of  the  bottom  of  the  filter. 

This  result  is  accomplished,  however,  at  a  great  loss  of  head 
in  the  wash  water.  When  a  filter  is  washed  from  the  pressure- 
mains  without  separate  pumping,  the  pressure  is  usually  sufficient 
and  there  is  no  disadvantage  in  the  arrangement.  When,  how- 
ever, the  water  is  specially  pumped  for  washing,  the  required  head 
is  much  greater  than  would  otherwise  be  necessary. 

It  would  not  be  possible  to  increase  the  size  of  the  necks, 
thereby  decreasing  the  friction,  without  increasing  very  largely  the 


5  c 


s    I 


MECHANICAL   FILTERS.  175 

size  of  the  pipes  in  the  underdrainage  system  into  which  the 
strainers  are  fastened.  These  pipes  are  so  small  that  during 
washing  the  velocity  in  them  is  about  13  feet  per  second,  and  if 
the  throats  of  the  necks  were  increased  without  also  enlarging 
these  pipes,  the  friction  would  be  so  reduced  that  most  of  the 
water  would  go  through  the  necks  nearest  the  supply,  thus  failing 
to  reach  the  object  to  be  attained. 

A  more  rational  system  would  be  to  increase  the  sizes  of  all 
the  waterways  in  the  outlet  and  wash- water  system.  The  Jewell 
filter  is  also  provided  with  a  rake  to  keep  the  sand  mixed  daring 
washing,  as  this  is  necessary  even  with  the  complete  distribution 
of  wash-water  over  the  area  of  the  filter. 

Both  the  Warren  and  the  Jewell  filters  are  provided  with 
receptacles  through  which  the  water  passes  after  receiving  the 
coagulant,  and  before  entering  the  filter.  In  the  Jewell  filter  the 
receptacle,  called  a  sedimentation-basin,  is  of  such  size  as  to  hold 
as  much  water  as  is  filtered  in  15  minutes.  In  the  Warren  filter 
the  receptacle  is  entirely  independent  and  larger,  holding  about 
an  hour's  supply. 

The  rates  of  filtration  used  in  the  experiments  have  ranged 
from  less  than  100  to  about  130  million  gallons  per  acre 
daily.  To  employ  a  rate  much  higher  than  this  involves  the 
use  of  a  much  coarser  sand,  or  an  increase  in  the  height  of 
water  upon  the  filter  to  an  impracticable  extent.  There  would 
seem  to  be  no  material  advantage  in  the  use  of  lower  rates 
within  certain  limits,  while  the  cost  of  filters  would  be  greatly 
increased. 

The  sand  used  in  the  Warren  filters  has  been  crushed  quartz. 
In  the  Jewell  filters  a  silicious  sand  from  Red  Wing,  Minn., 
with  rounded  grains  has  been  used.  These  sands  are  somewhat 
coarser  than  are  commonly  used  in  sand  filters,  and  the  uniformity 
coefficients  are  very  low.  It  is  necessary  to  use  sand  with  the 
very  lowest  uniformity  coefficients  to  avoid  the  separation  of  sand 
particles  according  to  sizes  as  mentioned  above,  and  for  this  reason 


PERFORATED  COPPER 

COVERING  EACH  OF 

THE  COLLECTING  TRAYS 


PRESSURE  WASH 


GUTTER  CASTING 


CEMENT  OVER 
GUTTER  PIPES 


PLAN  JUST  ABOVE  COPPER. 


SECTION' SHOWING  FILTER  DURING  ORDINARY  OPERATION. 

FIG.  23. — WARREN  FILTEB  :   PITTSBURG  EXPERIMENTS.     SECTION  No.  i. 


STAVES  OF  TANK 


FILLING  BETWEEN 
GUTTERS 


PLAN  OF  AGITATOR,  GUTTER  CASTINGS,  ETC. 


18  X  6«  CLUTCH 
PULLEY 


SECTION  SHOWING  FILTER  DURING  OPERATION  OF  WASHING. 
FIG.  24. — WARREN  FILTER  :    PITTSBURG  EXPERIMENTS.     SECTION  No.  2. 


i;8  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

the  sand  must  be  selected  with  much  greater  care  than  is  required 
for  sand  filters. 

The  round-grained  sand  is  more  readily  and  completely  washed 
than  the  angular  crushed  quartz.  It  has  been  claimed  that  the 
crushed  quartz  is  more  efficient  as  a  filtering  material,  but  the 
evidence  of  this  is  not  very  clear. 

The  amount  of  water  filtered  by  a  filter  between  washings  is, 
in  a  general  way,  about  the  same  as  that  filtered  by  a  sand  filter 
betweelh scrapings,  in  relation  to  its  area.  The  amount  of  water 
required  for  washing  is,  on  an  average,  about  equal  to  a  vertical 
column  5  or  6  feet  high  equal  in  area  to  the  area  of  the  filter, 
exclusive  of  water  on  the  top  of  the  filter  wasted  before  the  current 
is  reversed.  With  clear  waters,  as  for  instance,  the  Allegheny  at 
low  water,  the  amount  of  washing  is  almost  directly  proportional 
to  the  amount  of  sulphate  of  alumina  used.  With  muddy  waters 
the  sulphate  of  alumina  required  is  proportional  to  the  mud,  and 
the  frequency  of  washing  and  the  amount  of  wash-water  are  pro- 
portional to  both.  The  amount  of  wash-water  required  averages 
about  five  per  cent;  with  very  muddy  waters  more  is  required. 
At  Louisville,  with  the  worst  waters,  the  per  cents  of  wash-water 
rose  at  times  to  30  per  cent  of  the  total  quantity  of  water  filtered. 

The  rate  of  filtration  with  mechanical  filters  should  be  kept  as 
constant  as  possible,  and  can  be  regulated  by  devices  similar  to 
those  described  in  connection  with  sand  filters.  Owing  to  the 
smaller  areas  and  capacities,  the  amounts  of  water  to  be  handled 
in  the  units  are  smaller,  and  the  regulating  devices  are  thus  smaller, 
and  have  always  been  made  of  metal,  either  cast  iron  or  copper. 
None  of  the  devices  employed  in  the  above-mentioned  experi- 
ments has  been  entirely  satisfactory  in  this  respect.  The  devices 
employed  have  been  too  small,  and  the  water  has  gone  through  at 
top  high  velocities  to  allow  close  adjustment. 

As  between  the  two  types  of  filters,  the  Jewell  filter  requires  a 
large  loss  of  head.  The  water  has  to  be  pumped  at  a  sufficient 
elevation  to  reach  the  top  of  a  tank  about  18  feet  high,  while  the 


M ECU  A  ML  A  I.    FILTERS.  179 

effluent  must  be  drawn  off  at  the  extreme  bottom.  The  Warren 
filter  is  much  more  economical  in  head,  the  plants  at  Pittsburgand 
Louisville  only  requiring  about  9  feet  from  the  inlet  to  the  outlet. 
The  earlier  mechanical  filters  were  usually  constructed  of 
wrought  iron  or  steel  plates.  More  recently  wooden  tanks  have 
been  commonly  employed,  although  steel  is  regarded  as  preferable. 
Concrete  or  masonry  tanks  have  been  suggested,  but  they  have 
not  as  yet  been  employed. 

EFFICIENCY   OF   MECHANICAL   FILTERS. 

The  efficiency  of  mechanical  filters  depends  entirely  upon  the 
use  of  coagulants.  Without  coagulants  they  can  only  be  used  to 
remove  very  large  particles.  The  efficiency  of  the  filtration  depends 
much  more  upon  the  kind,  and  amount,  and  method  of  application 
of  coagulant  than  upon  the  arrangement  of  the  filter.  In  fact,  the 
arrangements  of  the  filter  are  more  directed  to  the  convenience 
and  economy  of  operation  and  washing  than  towards  the  efficiency 
of  the  results. 

The  conditions  which  control  the  efficiency  of  mechanical  filters 
have  been  discussed  in  connection  with  coagulation.  With  suffi- 
cient coagulant  the  removal  of  turbidity  or  mud  is  complete. 
Color  also  can  be  removed  with  these  filters.  The  bacterial 
efficiencies  secured  with  them  have  been  discussed  at  length  in 
connection  with  the  Pittsburg  experiments. 

With  careful  coagulation  and  manipulation  it  is  possible  to  get 
98  per  cent  bacterial  efficiency  without  difficulty.  The  results  are 
somewhat  irregular,  for  reasons  not  as  yet  fully  understood.  On 
some  occasions  higher  bacterial  efficiencies  are  secured  with  smaller 
quantities  of  coagulant,  while  at  other  times  the  efficiencies  are 
less  without  apparent  reason.  There  seems  to  be  a  limit  to  the 
bacterial  efficiency  which  can  be  secured  with  any  amount  of  sul- 
phate of  alumina  and  rapid  filtration,  and  it  is  doubtful  if  a  plant 
could  be  operated  to  regularly  secure  as  high  a  bacterial  efficiency 
as  99  per  cent  with  any  amount  of  sulphate  of  alumina. 


'ISO  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


PRESSURE   FILTERS. 

Pressure  mechanical  filters  are  constructed  in  entirely  closed 
receptacles,  through  which  the  water  is  forced  under  pressure  and 
,not  by  gravity.  Many  of  the  earlier  mechanical  filters  were  of 
this  type.  In  small  plants  this  system  has  the  distinct  advantage 
that  the  water  can  be  pumped  from  a  river  or  other  source  of  sup- 
ply through  a  filter  direct  to  the  reservoir  or  into  the  mains,  while 
any  other  system  would  involve  a  second  pumping.  Pressure 
filters  are  extensively  used  for  hotel  supplies,  etc.,  where,  from 
the  conditions,  gravity  filters  are  impossible.  The  practical  objec- 
tions to  this  system  have  been  found  to  be  so  great  that  it  is  rarely 
used  tinder  other  conditions.  Some  experiments  were  made  at 
Louisville  with  a  filter  of  this  type,  but  they  were  not  long  con- 
tinued, and  aside  from  them  there  is  no  precise  information  as  to 
what  can  be  accomplished  with  filters  of  this  type. 


OTHER  METHODS   OF  FILTRATION,  l8l 


CHAPTER    XI. 
OTHER   METHODS   OF   FILTRATION. 

WORMS   TILE    SYSTEM. 

THIS  system,  invented  and  patented  by  Director  Fischer  of 
the  Worms  water-works,  consists  of  the  filtration  of  water  through 
artificial  hollow  sandstone  tiles,  made  by  heating  a  mixture  of 
broken  glass  and  sand,  sifted  to  determined  sizes,  to  a  point  just 
below  the  melting-point  of  the  glass,  in  suitable  moulds  or  forms. 
The  glass  softens  and  adheres  to  the  sand,  forming  a  strong 
porous  substance  through  which  water  can  be  passed.  These  tiles 
are  made  hollow  and  are  immersed  in  the  water  to  be  treated,  the 
effluent  being  removed  from  the  centre  of  each  tile.  They  are 
connected  together  in  groups  corresponding  in  size  to  the  units  of 
a  sand-filtration  plant.  They  are  washed  by  a  reverse  current  of 
filtered  water.  These  tiles  have  been  used  for  some  years  at 
Worms,  Germany,  and  at  a  number  of  smaller  places,  and  were 
investigated  experimentally  at  Pittsburg.  Some  difficulty  has 
been  experienced  in  getting  tiles  with  pores  small  enough  to  yield 
an  effluent  of  the  desired  purity,  and  at  the  same  time  large 
enough  to  allow  a  reasonable  quantity  of  water  to  pass.  In  fact, 
with  other  than  quite  clear  waters,  it  has  not  been  found  feasible 
to  accomplish  both  objects  at  the  same  time,  and  it  has  been 
necessary  to  treat  the  water  with  coagulants  and  preliminary 
sedimentation  or  filtration  before  applying  it  to  the  tiles.  The 
problem  of  making  the  joints  between  the  tiles  and  the  collection- 
pipes  water-tight  when  surrounded  by  the  raw  water  also  is  a 
matter  of  some  difficulty. 

THE   USE   OF   ASBESTOS. 

It  has  been  suggested  by  Mr.  P.  A.  Maignen  that  the  surface 
of  sand  filters  should  be  covered  with  a  thin  layer  of  asbestos, 


1 82  FILTRATION  OF  PUBLIC   WAITER-SUPPLIES. 

applied  in  the  form  of  a  pulp,  with  the  first  water  put  onto  the 
filter  after  scraping.  The  asbestos  forms  a  sort  of  a  paper  on  the 
sand  which  intercepts  the  sediment  of  the  passing  water.  The 
advantage  of  the  process  is  in  the  cleaning.  When  dried  to  the 
right  consistency  this  asbestos  can  be  rolled  up  like  a  carpet,  and 
taken  from  the  filter  without  removing  any  of  the  sand. 

This  procedure  is  almost  identical  with  that  which  has  occurred 
naturally  in  iron-removal  plants,  where  algae  grow  in  the  water 
upon  the  filters,  and  form  a  fibrous  substance  with  the  ferric  oxide 
removed  from  the  water,  which  can  be  rolled  up  and  removed  in 
the  same  way  as  the  asbestos.  The  advantages  of  the  process, 
from  an  economical  standpoint,  are  less  clear. 

FILTERS    USING    HIGH    RATES    OF    FILTRATION   WITHOUT 
COAGULANTS. 

Numerous  filters  have  been  suggested,  and  a  few  have  been 
constructed  for  the  use  of  much  higher  rates  of  filtration  than  are 
usually  employed  with  sand  filters,  but  without  the  use  of  coagu- 
lants. The  results  obtained  depend  upon  the  requirements  and 
upon  the  character  of  the  raw  water.  If  a  reservoir  water  contains 
an  algae  growth,  it  can  often  be  removed  by  a  coarse  and  rapid 
filter.  The  organisms  in  this  case  are  many  times  larger  than  the 
bacteria,  and  many  times  larger  than  the  clay  particles  which  con- 
stitute turbidity.  The  requirements  in  this  case  are  rather  in  the 
nature  of  straining  than  of  filtration. 

The  conditions  necessary  for  the  removal  of  bacteria  and 
turbidity  are  very  well  understood,  and  it  can  be  stated  with 
the  utmost  confidence  that  no  system  of  filtration  through 
sand  at  rates  many  times  as  high  as  are  used  in  ordinary  sand 
filtration,  and  without  the  use  of  coagulants,  will  be  satisfactory 
where  either  bacterial  efficiency  or  clarification  is  required.  The 
application  of  such  systems  of  filtration  would  therefore  seem  to 
be  somewhat  limited. 


>^«™"^ 

UNIVERSITY 


OTHER   METHODS    OF  FILTRATION.  183 

HOUSEHOLD    FILTERS. 

The  subject  of  household  filters  is  a  somewhat  broad  one,  as 
the  variety  in  these  filters  is  even  greater  than  in  the  larger 
filters,  and  the  range  in  the  results  to  be  expected  from  them  is 
at  least  as  great.  I  shall  only  attempt  to  indicate  here  some  of 
the  leading  points  in  regard  to  them. 

Household  filters  may  be  used  to  remove  mud  or  iron  rust 
from  the  tap  water,  or  to  remove  the  bacteria  in  case  the  latter 
is  sewage-polluted,  or  to  do  both  at  once.  Perhaps  oftener  they 
are  used  simply  because  it  is  believed  to  be  the  proper  thing,  and 
without  any  clear  conception  either  of  the  desired  result  or  the 
way  in  which  it  can  be  accomplished.  I  shall  consider  them 
only  in  their  relations  to  the  removal  of  bacteria,  as  I  credit  the 
people  who  employ  them  with  being  sufficiently  good  judges  of 
their  efficiency  in  removing  visible  sediment. 

In  the  first  place,  as  a  general  rule,  which  has  very  few  if 
any  exceptions,  we  may  say  that  all  small  filters  which  allow  a 
good  stream  of  water  to  pass  do  not  remove  the  bacteria.  The 
reason  for  this  is  simply  that  a  material  open  enough  to  allow 
water  to  pass  through  it  rapidly  is  not  fine  enough  to  stop  such 
small  bodies  as  the  bacteria.  The  filters  which  are  so  often  sold 
as  "  germ-proof,"  consisting  of  sand,  animal  charcoal,  wire-cloth, 
filter-paper,  etc.,  do  not  afford  protection  against  any  unhealthy 
qualities  which  there  may  be  in  the  raw  water.  Animal  charcoal 
removes  color  without  retaining  the  far  more  objectionable 
bacteria. 

The  other  household  filters  have  filtering  materials  of  much 
finer  grain,  unglazed  porcelain  and  natural  sandstone  being  the 
most  prominent  materials,  while  infusorial  earth  is  also  used. 
The  smaller  sizes  of  these  filters  allow  water  to  pass  only  drop  by 
drop,  and  when  a  fair  stream  passes  them  the  filters  have  consid- 
erable filtering  area  (as  a  series  of  filter-tubes  connected  together). 
On  account  of  their  slow  action,  filters  of  this  class  are,  as  a  rule, 
provided  with  storage  reservoirs  so  that  filtered  water  to  the 


1 84  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

capacity  of  the  reservoir  can  be  drawn  rapidly  (provided  the 
calls  do  not  come  too  often).  Some  of  these  filters  are  nearly 
germ-proof,  and  are  comparable  in  their  efficiency  to  large  sand- 
filters.  There  is  no  sharp  line  between  the  filters  which  stop 
and  which  do  not  stop  the  bacteria  ;  but  in  general  the  rule  that 
a  filter  which  works  rapidly  in  proportion  to  its  size  does  not  do 
so,  and  vice  versa,  will  be  found  correct. 

In  thinking  of  the  efficiency  of  household  filters  we  must  dis- 
tinguish between  the  filter  carefully  prepared  for  an  award  at  an 
exhibition  and  the  filter  of  the  same  kind  doing  its  average 
daily  work  in  the  kitchen.  If  we  could  be  sure  in  the  latter  case 
that  an  unbroken  layer  of  fine  sandstone  or  porcelain  was  always 
between  ourselves  and  the  raw  tap- water  we  could  feel  compara- 
tively safe.  The  manufacturers  ol  the  filters  claim  that  leaky 
joints,  cracked  tubes,  etc.,  are  impossible  ;  but  I  would  urge  upon 
the  people  using  water  filtered  in  this  way  that  they  personally 
assure  themselves  that  this  is  actually  the  case  with  their  own 
filters,  for  in  case  any  such  accident  should  happen  the  conse- 
quences might  be  most  unpleasant.  The  increased  yield  of  a 
filter  due  to  a  leaky  joint  is  sure  not  to  decrease  it  in  favor  with 
the  cook,  who  is  probably  quite  out  of  patience  with  it  because 
it  works  so  slowly,  that  is,  in  case  it  is  good  for  anything. 

The  operation  of  household  filters  is  necessarily,  with  rare  ex- 
ceptions, left  to  the  kitchen-girl  and  luck.  Scientific  supervision 
is  practically  impossible.  With  a  large  filter,  on  the  other  hand, 
concentrating  all  the  filters  for  the  city  at  a  single  point,  a  com- 
petent man  can  be  employed  to  run  them  in  the  best-known 
way ;  and  if  desired,  and  as  is  actually  done  in  very  many  places, 
an  entirely  independent  bacteriologist  can  be  employed  to  deter- 
mine the  efficiency  of  filtration.  With  the  methods  of  examina- 
tion now  available,  and  a  little  care  in  selecting  the  times  and 
places  of  collecting  the  samples,  it  is  quite  impossible  for  a  filter- 
superintendent  to  deliver  a  poor  effluent  very  often  or  for  any 
considerable  length  of  time  without  being  caught.  The  safety 
of  properly-conducted  central  filtration  is  thus  infinitely  greater 


OTHER   METHODS   OF  FILTRATION.  1 85 

than  that  from  even  the  best  household  filters.  Further,  it  may 
be  doubted  whether  an  infected  water  can  be  sent  into  every 
house  in  the  city  to  be  used  for  washing  and  all  the  purposes 
to  which  water  is  put  except  drinking,  without  causing  disease,, 
although  less  than  it  would  if  it  were  also  used  for  drinking. 

The  use  of  household  filters  must  be  regarded  as  a  somewhat 
desperate  method  of  avoiding  some  of  the  bad  consequences  of 
a  polluted  water-supply,  and  they  are  adopted  for  the  most  part 
by  citizens  who  in  some  measure  realize  the  dangers  from  bad 
water,  but  who  cannot  persuade  their  fellow-citizens  to  a  more 
thorough  and  adequate  solution  of  the  problem.  Such  citizens, 
by  the  use  of  the  best  filters,  and  by  carefully  watching  their 
action,  or  by  having  their  drinking-water  boiled,  can  avoid  the 
principal  dangers  from  bad  water,  but  their  vigilance  does  not 
protect  their  more  careless  neighbors. 


1 86  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


CHAPTER    XII. 
REMOVAL  OF   IRON    FROM   GROUND-WATERS. 

THE  filtration  of  ground-waters  is  a  comparatively  recent 
development.  Ground-waters  are  filtered  by  their  passage  through 
soil  generally  much  more  perfectly  than  it  is  possible  to  filter  other 
waters,  and  any  further  filtration  of  them  is  useless.  Such  waters, 
however,  occasionally  contain  iron  in  solution  as  ferrous  carbonate. 

Waters  containing  iron  have  been  used  as  mineral  waters  for  a 
very  long  time.  Such  waters  have  an  astringent  taste,  and  have 
been  esteemed  for  some  purposes.  As  ordinary  water-supplies, 
however,  they  are  objectionable.  The  iron  deposits  in  the  pipes 
when  the  current  is  slow,  and  is  flushed  out  when  it  is  rapid,  and 
makes  the  water  turbid  and  disagreeable ;  and  still  worse,  the  iron 
often  gets  through  the  pipe-system  in  solution,  and  deposits  in  the 
wash-tub,  coloring  the  linen  a  rusty  brown  and  quite  spoiling  it. 

An  organism  called  crenothrix  grows  in  pipes  carrying  waters 
containing  iron,  and  after  a  while  this  organism  dies,  and  decom- 
poses, and  gives  rise  to  very  disagreeable  tastes  and  odors.  It 
thus  happens  that  ground-waters  containing  iron  are  unsatisfactory 
as  public  water-supplies,  and  are  sources  of  serious  complaint. 

AMOUNT     OF     IRON     REQUIRED     TO     RENDER     WATER 
OBJECTIONABLE. 

Three  hundredths  of  a  part  in  100,000  of  metallic  iron  very 
rarely  precipitate  or  cause  any  trouble.  Five  hundredths  occa- 
sionally precipitate,  and  this  amount  may  be  taken  as  about  the 
allowable  limit  of  iron  in  a  satisfactory  water.  One  tenth  of  a 
part  is  quite  sure  to  precipitate  and  give  rise  to  serious  complaint. 
Two  or  three  tenths  make  the  water  entirely  uns?  ^ble  for 


REMOVAL    OF  IRON  FROM  GROUND-WATERS.  187 

laundry  purposes,  and  are  otherwise  seriously  objectionable,  and 
will  hardly  be  tolerated  by  a  community.  Under  some  conditions 
ground-waters  carry  as  much  as  I  part  in  100,000  of  iron,  and  such 
waters  are  hardly  usable.  In  iron-removal  plants  an  effluent  con- 
taining less  than  0.05  is  regarded  as  satisfactory.  One  containing 
less  than  0.02,  as  is  the  case  with  many  plants,  is  all  that  can  be 
desired.  The  percentage  of  removal  is  of  no  significance,  but 
only  the  amount  left  in  the  effluent. 

CAUSE    OF   IRON    IN    GROUND-WATERS. 

Natural  sands,  gravels,  and  rocks  almost  always  contain  iron, 
often  in  considerable  amount.  The  iron  is  usually  combined  with 
oxygen  as  ferric  oxide,  and  in  this  condition  it  is  insoluble  in 
water.  Water  passing  through  iron  containing  materials  will  not 
ordinarily  take  up  iron.  When,  however,  the  water  contains  a 
large  amount  of  organic  matter  in  solution,  this  organic  matter 
takes  part  of  the  oxygen  away  from  the  iron,  and  reduces  the 
ferric  oxide  to  ferrous  oxide.  The  ferrous  oxide  combines  with 
carbonic  acid,  always  present  under  these  conditions,  forming  fer- 
rous carbonate,  which  is  soluble  and  which  goes  into  solution. 

Surface-waters  nearly  always  carry  free  oxygen,  and  when  such 
waters  enter  the  ground  they  carry  oxygen  with  them,  and  the 
organic  matters  in  the  water  use  up  the  free  oxygen  before  they 
commence  to  take  oxygen  away  from  the  iron  of  the  ground.  It 
is  thus  only  in  the  presence  of  organic  matters,  and  in  the  absence 
of  free  oxygen,  that  the  solution  of  iron  is  possible.  It  sometimes 
happens  that  the  organic  matters  which  reduce  the  iron  are  con- 
tained in  the  soil  itself,  in  which  case  iron  may  be  taken  up  even 
by  water  originally  very  pure,  as  for  instance,  by  rain-water. 

Generally  speaking,  iron  is  everywhere  present  in  sufficient 
quantity  in  the  strata  from  which  ground-waters  are  obtained,  and 
wherever  the  conditions  of  the  organic  matters  and  oxygen  neces- 
sary for  solution  occur,  iron-containing  waters  are  secured,  and  the 
iron  is  usually  present  in  the  earth  in  such  quantity  that  the  water 


1 88  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

can  dissolve  as  much  as  it  will  take  up  for  a  long  series  of  years, 
or  for  centuries,  without  exhausting  the  supply.  There  is  thus 
little  prospect  of  improvement  of  such  waters  from  exhaustion  of 
the  supply  of  iron. 

The  circumstances  which  control  the  solution  of  iron  are  very 
complicated  and  difficult  to  determine.  Wells  near  a  river,  and 
drawing  their  water  largely  from  it  by  seepage,  are  apt  to  yield  a 
water  containing  iron  sooner  or  later,  especially  where  the  river- 
water  carries  a  large  amount  of  organic  matter  in  solution.  Waters 
drawn  from  extensive  gravel  deposits,  in  which  the  water  is 
renewed  principally  by  the  rainfall  upon  the  surface  of  the  deposits 
themselves,  often  remain  entirely  free  from  iron  indefinitely.  The 
rain-water  is  almost  free  from  organic  matter,  and  the  air  is  able 
to  take  care  of  decomposing  organic  matters  in  the  surface  soil, 
and  below  this  there  are  no  accumulations  of  organic  matter  suffi- 
cient to  cause  the  solution  of  iron.  Under  other  conditions  there 
are  subterranean  sources  of  organic  matter  which  result  in  the 
solution  of  iron  under  conditions  which,  on  the  surface,  appear 
most  favorable  for  securing  good  water.  Wells  are  often  used  for 
many  years-  without  developing  iron,  when  suddenly  iron  will 
appear.  This  appearance  of  iron  is  often  connected  with  increas- 
ing consumption  of  water.  In  some  cases  it  may  result  from 
drawing  water  from  areas  not  previously  drawn  upon. 

WThen  iron  once  makes  its  appearance  in  a  water,  it  seldom 
disappears  completely  afterward,  although  it  often  fluctuates 
widely  at  different  seasons  of  the  year  and  under  different  condi- 
tions of  pumping.  In  some  cases  a  decrease  in  the  quantity  of 
iron  is  noted  after  a  number  of  years,  but  in  other  cases  this  does 
not  happen. 

In  a  few  cases  manganese  has  been  found  in  ground-waters 
Manganese  in  water  behaves  much  like  iron,  but  there  are  some 
points  of  difference,  so  that  the  possibility  of  the  presence  of  this 
substance  should  be  borne  in  mind. 

Iron-containing  waters  are  generally  entirely  free  from  oxygen, 


REMOVAL    OF  IRON  FROM  GROUND-WATERS.  189 

and  when  first  drawn  from  the  ground  they  are  bright  and  clear 
and  do  not  differ  in  appearance  from  other  ground-waters.  On 
exposure  to  the  air  they  quickly  become  turbid  from  the  oxidation 
of  the  iron,  and  its  precipitation  as  ferric  hydrate.  At  West 
Superior,  Wisconsin,  a  water  was  found  containing  both  iron  and 
dissolved  oxygen.  It  was  turbid  as  pumped  from  the  well.  This 
condition  of  affairs  seemed  abnormal,  but  was  repeatedly  checked, 
and  the  theory  was  advanced  by  Mr.  R.  S.  Weston,  who  made 
the  observations,  that  it  resulted  from  a  mixture  in  the  wells  of 
two  entirely  different  waters,  namely,  a  water  resulting  from  the 
rainfall  on  sand  deposits  back  of  the  wells,  containing  dissolved 
oxygen  and  no  iron,  and  water  from  the  lake  which  had  seeped 
through  the  sand,  and  which  contained  a  considerable  amount  of 
iron  in  solution  but  no  dissolved  oxygen.  The  wells  thus  drew 
water  from  opposite  directions,  and  the  two  waters  were  entirely 
different  in  character,  and  the  mixture  thus  had  a  composition 
which  would  not  have  been  possible  in  a  water  all  of  which  came 
from  a  single  source. 

TREATMENT   OF   IRON-CONTAINING   WATERS. 

The  removal  of  iron  from  ground-water  is  ordinarily  a  very 
simple  procedure.  It  is  simply  necessary  to  aerate  the  water,  by 
which  process  the  ferrous  carbonate  is  decomposed,  and  oxidized 
with  the  formation  of  ferric  hydrate,  which  forms  a  flocculent 
precipitate  and  is  readily  removed  by  filtration.  The  aeration 
required  varies  in  different  cases.  The  quantity  of  oxygen  re- 
quired to  oxidize  the  iron  is  only  a  small  fraction  of  the  amount 
which  water  will  dissolve,  and  allowing  water  to  simply  fall 
through  the  air  for  a  few  feet  in  fine  streams  will  usually  supply 
several  times  as  much  oxygen  as  is  necessary  for  this  purpose. 

Aerating  devices  of  this  kind  have  proved  sufficient  in  a 
number  of  cases,  as  at  Far  Rockaway,  L.  I.,  and  at  Red  Bank, 
N.  J.  In  some  cases,  however,  a  further  aeration  is  necessary, 
not  for  the  purpose  of  getting  more  oxygen  into  the  water, 


190  FIL  TRA  T1ON  OF  P UBLIC    WA  TER-SUPPLIES. 

but  to  get  the  excess  of  carbonic  acid  out  of  it.  Carbonic  acid 
seems  to  retard  in  some  way  the  oxidation  of  the  iron,  and  it  is 
occasionally  present  in  ground-waters  in  considerable  quantity,  and 
quite  seriously  interferes  with  the  process.  It  can  be  removed 
sufficiently  by  aeration,  but  the  necessary  amount  of  exposure  to 
air  is  much  greater  than  that  required  to  simply  introduce  oxygen. 

Coke-towers  have  sometimes  been  used  for  this  purpose.  The 
towers  are  filled  with  coarse  coke  and  have  open  sides,  and  water 
is  sprinkled  over  the  tops  of  them  and  allowed  to  drip  through  to 
the  bottoms.  In  general  the  simple  exposure  of  water  to  the  air 
for  a  sufficient  length  of  time,  in  any  form  of  apparatus  or  simply 
in  open  channels,  will  accomplish  the  desired  results. 

Mr.  H.  W.  Clark*  has  called  attention  to  the  fact  that  in 
some  cases  coke  seems  to  have  a  direct  chemical  action  upon  the 
water  which  is  entirely  independent  of  its  aerating  effect.  In  his 
experiments  there  seemed  to  be  some  property  in  the  coke  which 
caused  the  iron  to  oxidize  and  flocculate  in  many  cases  when  it 
refused  to  do  so  with  simple  aeration  and  filtration. 

When  the  right  conditions  are  reached  the  oxidation  of  the 
iron  is  very  rapid,  and  it  separates  out  in  flakes  of  such  size  that 
they  can  be  removed  by  filtration  at  almost  any  practicable  rate. 
Mechanical  filters  have  been  used  for  this  purpose,  with  rates  of 
filtration  of  100  million  gallons  per  acre  daily.  In  Germany,, 
where  plants  for  the  removal  of  iron  are  quite  common,  modified 
forms  of  sand  filters  have  usually  been  employed  which  have  been 
operated  at  rates  up  to  25  million  gallons  per  acre  daily. 

In  experiments  made  by  the  Massachusetts  State  Board  of 
Health  rates  from  10  to  25  million  gallons  per  acre  daily  have 
been  employed. 

The  sand  used  for  filtration  may  appropriately  be  somewhat 
coarser  than  would  be  used  for  treating  surface-waters,  and  tluv 
thickness  of  the  sand  layer  may  be  reduced.  Owing  to  the  higher 

*  "  Removal  of   Iron    from   Ground   Waters,"   Journal   of  the   New   England 
Water  Works  Association,  Vol.  xi,  1897,  page  277. 


REMOVAL    OF  IRON  FROM  GROUND-WATERS.  19! 

rates  the  underdrainage  system  must  be  more  ample  than  is  other- 
wise necessary. 

The  rate  of  filtration  employed  is  usually  not  a  matter  of  vital 
importance,  but  by  selecting  a  rate  that  is  not  too  high  it  is  possi- 
ble to  use  a  moderate  loss  of  head.  It  is  thus  not  necessary  to 
clean  the  filters  too  often,  and  the  expenses  of  operation  are  not 
as  high  as  with  an  extreme  rate.  In  some  cases  it  is  desired  to 
accomplish  other  results  than  the  removal  of  iron  by  filtration, 
and  this  may  lead  to  the  selection  of  a  rate  lower  than  would 
otherwise  be  used. 

Under  normal  conditions  of  operation  all  of  the  iron  separates 
on  the  top  of  the  sand.  No  appreciable  amount  of  it  penetrates 
the  sand  at  all.  With  open  filters  at  Far  Rockaway  and  at  Red 
Bank  there  is  an  algae  growth  in  the  water  upon  the  filters  which, 
with  the  iron,  forms  a  mat  upon  the  surface  of  the  filter;  and 
when  the  filter  is  put  out  of  service  and  allowed  to  partially  dry, 
this  mat  can  be  rolled  up  like  a  carpet  and  thrown  off  without 
removing  any  sand,  and  the  filters  have  been  in  use  for  several 
years  without  renewing  any  sand  and  without  any  important 
decrease  in  the  thickness  of  the  sand  layer. 

Some  waters  contain  iron  in  such  a  form  that  it  cannot  be  suc- 
cessfully removed  in  this  manner.  Thus  at  Reading,  Mass.,  it 
was  reported  by  Dr.  Thomas  M.  Drown  that  the  iron  was  present 
in  the  form  of  ferrous  sulphate  instead  of  ferrous  carbonate,  and 
that  it  was  not  capable  of  being  separated  by  simple  aeration  and 
filtration.  A  Warren  mechanical  filter  was  installed,  and  the  water 
is  treated  by  aeration  and  with  the  addition  of  lime  and  alum. 
The  cost  of  the  process  is  thereby  much  increased,  and  the  hard- 
ness of  the  water  is  increased  threefold. 

Several  other  cases  have  been  reported  where  it  was  believed 
that  simple  aeration  and  filtration  were  inadequate;  but  the  ad- 
vantages of  the  simple  procedure  are  so  great  as  to  make  it  worth 
a  very  careful  study  to  determine  if  more  complete  aeration,  or  the 
use  of  coke-towers  and  perhaps  slower  filtration,  would  not  serve 


FILTRATION-  OF  PUBLIC    WATER-SUPPLIES. 

in  these  cases  without  resorting  to  the  use  of  chemicals  and  their 
attendant  disadvantages. 

IRON-REMOVAL   PLANTS    IN    OPERATION. 

Iron-removal  plants  are  now  in  use  at  Amsterdam  and  The 
Hague  in  Holland,  at  Copenhagen  in  Denmark,  at  Kiel,  Char- 
lottenburg,  Leipzig,  Halle,  and  many  other  places  in  Germany; 
at  Reading,  Mass. ;  Far  Rockaway,  L.  I. ;  Red  Bank,  Asbury 
Park,  Atlantic  Highlands,  and  Keyport,  N.  J. 

Among  the  earliest  plants  for  the  removal  of  iron  were  the 
filters  constructed  at  Amsterdam  and  The  Hague  in  Holland.  At 
Amsterdam  the  water  is  derived  from  open  canals  in  the  dunes 
draining  a  large  area.  The  water  has  its  origin  in  the  rain-water 
falling  upon  the  sand.  The  sand  is  very  fine  and  contains  organic 
matter  in  sufficient  amount  so  that  the  ground-water  is  impreg- 
nated with  iron.  In  flowing  to  a  central  point  in  the  open  canals 
the  water  becomes  aerated  and  the  iron  oxidized.  There  are  also 
algae  growths  in  the  water  which  perhaps  aid  the  process.  Sand 
filters  of  ordinary  construction  are  used,  and  remove  both  the  iron 
and  the  algae,  and  the  rate  of  filtration  is  not  higher  than  is  usually 
used  in  the  treatment  of  river-waters,  although  it  could  probably 
be  largely  increased  without  detriment  to  the  supply. 

The  works  at  The  Hague  are  very  similar  to  those  at  Amster- 
dam, but  covered  collectors  are  used  to  supplement  the  open  canals. 
Both  of  these  plants  were  built  before  much  was  known  about  iron 
in  ground-waters  and  the  means  for  its  removal,  but  they  have 
performed  their  work  with  uniformly  satisfactory  results.  In  the 
more  recent  German  works  various  aerating  devices  are  employed, 
and  filters  similar  in  general  construction  to  ordinary  sand  filters, 
but"  with  larger  connections  suited  to  very  high  rates  of  filtration, 
are  employed. 

The  plant  at  Asbury  Park  was  the  first  of  importance  con- 
structed in  America.  The  water  is  raised  from  wells  from  400  to 
noo  feet  deep  by  compressed  air  by  a  Pohle  lift.  It  is  delivered 


REMOVAL    OF  IRON  FROM  GROUND-WATERS.  IQ3 

into  a  square  masonry  receiving-basin  holding  some  hours'  supply. 
The  aeration  of  the  water  by  this  means  is  very  complete.  It  is 
afterwards  pumped  through  Continental  pressure  filters  direct  into 
the  service-pipes.  The  reservoir  for  the  aerated  water  was  not  a 
part  of  the  original  plant,  but  was  added  afterwards  to  facilitate 
operation,  and  to  give  more  complete  aeration  before  filtration. 

At  Far  Rockaway,  L.  I.,  the  water  is  lifted  from  wells  by  a 
\Vorthington  Pump,  and  is  discharged  over  the  bell  of  a  vertical 
i6-inch  pipe,  from  which  it  falls  through  the  air  to  the  water  in  a 
receiving  chamber  around  it.  The  simple  fall  through  the  air 
aerates  the  water  sufficiently.  From  the  receiving-chamber  the 
water  is  taken  to  either  or  both  of  two  filters,  each  with  an  area 
of  20,000  square  feet.  These  filters  are  open,  with  brick  walls 
and  concrete  bottoms,  three  feet  of  sand  and  one  foot  of  gravel, 
and  the  underdrains  are  of  the  usual  type.  The  water  flows 
through  regulator-chambers  to  a  well  25  feet  in  diameter  and  12 
feet  deep,  from  which  it  is  pumped  to  a  stand-pipe  in  the  town. 
The  plant  was  built  to  treat  easily  three  million  gallons  per  day, 
and  has  occasionally  treated  a  larger  quantity.  Either  filter  yields 
the  whole  supply  while  the  other  is  being  cleaned.  The  rate  of 
filtration  in  this  case  was  made  lower  than  would  have  otherwise 
been  necessary,  as  there  was  an  alternate  supply,  namely,  the 
water  from  two  brooks,  which  could  be  used  on  occasions,  and  to 
purify  which  a  lower  rate  of  filtration  was  regarded  necessary,  than 
would  have  been  required  for  the*  well-water.  The  removal  of 
iron  is  complete. 

The  plant  of  the  Rumson  Improvement  Company  at  Red 
Bank,  N.  J.,  is  quite  similar  to  that  at  Far  Rockaway,  but  is  much 
smaller.  The  outlet  is  a  6-inch  pipe  perforated  with  £-inch  holes 
which  throws  the  water  out  in  a  pine-tree  shape  to  the  receiving- 
tank,  thoroughly  aerating  it.  Each  of  the  two  filters  has  770 
square  feet  of  area.  The  filtering  material  is  three  feet  of  beach 
sand.  From  the  regulator-chamber  the  water  flows  to  a  circular 
well  1 8  feet  in  diameter,  covered  by  a  brick  dome  and  holding 


194 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


Section  on  A-B. 


IRON  RLMOVAL  PLANT.   RUMSON  IMPROVEMENT  COf  RED  BANK JN.J: 


FIG.  25. 

17,000  gallons,  from  which  it  is  pumped  to  the  stand-pipe.  Either 
of  the  filters  will  treat  ten  thousand  gallons  of  water  per  hour, 
which  is  equal  to  the  capacity  of  the  pumps;  and  as  the  consump- 


REMOVAL    OF  IRON  FROM  GROUND-WATERS.  IQ5 

tion  is  considerably  less  than  this  figure,  they  are  only  in  use  for 
a  part  of  each  day,  the  number  of  hours  depending  upon  the  con- 
sumption. These  filters  are  shown  by  the  accompanying  plan.. 
The  cost  of  the  work  was  as  follows: 

Filters  and   pure-water  reservoir,  with  piping 

and  drains  complete $3,799.47 

New  pump  and  connections 492.68 

Engineering  and  superintendence 992.91 


Total  cost  of  plant $5,285.06 

The  engineer  who  operates  the  pumps  takes  care  of  the  filters,, 
and  no  additional  labor  has  been  required.  The  entire  cost  of 
operation  is  thus  represented  by  the  additional  coal  required  for 
the  preliminary  lift  from  the  wells  to  the  filters.  The  effluent  is 
always  free  from  iron. 

The  plant  at  Reading,*  Mass.,  was  installed  by  the  Cumber- 
land Manufacturing  Company,  and  combines  aeration,  treatment 
with  lime  and  sulphate  of  alumina  and  rapid  filtration.  The 
aeration  is  effected  by  pumping  air  through  the  water,  after  the 
water  has  received  the  lime.  It  afterwards  receives  sulphate  of 
alumina  and  passes  to  a  settling-tank  holding  40,000  gallons,  in 
which  the  water  remains  for  about  an  hour.  There  are  six  filters 
of  the  Warren  type,  each  with  an  effective  filtering  area  of  54 
square  feet. 

The  cost  of  coagulant  is  considerable.  The  chief  disadvantage 
of  the  process  is  that  it  hardens  the  water,  which  is  naturally  soft. 
From  the  completion  of  the  plant  in  July,  1896,  to  the  end  of  the 
year  the  hardness  of  the  water  was  increased,  according  to  analyses 
of  the  State  Board  of  Health,  from  4.1  to  11.3  parts  in  100,000, 
and  for  the  year  1897  the  increase  was  from  4.0  to  12.7.  The 
iron,  which  is  present  in  the  raw  water  to  the  extent  of  about  0.26 
part  in  100,000,  is  removed  sufficiently  at  all  times. 

*  Journal  of  the  New  England  Water  Works  Association,  Vol.  ii,  pa.^r    r^u. 
Description  of  plant  by  Supt.  Lewis  M.  Bancroft. 


196  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

Prior  to  the  erection  of  this  plant  Mr.  Desmond  FitzGerald 
advised  aeration  followed  by  sedimentation  in  two  reservoirs  hold- 
ing half  a  million  gallons  each,  and  by  rapid  filtration.  Mr.  Ban- 
croft states  that  in  his  opinion,  if  the  reservoir  recommended  by 
Mr.  FitzGerald  had  been  built,  the  filters  could  be  run  with  very 
little  or  no  coagulation,  and  consequently  without  increase  in  hard- 
ness, which  is  the  most  obvious  disadvantage  to  the  procedure. 
The  nominal  capacity  of  the  plant  is  one  million  gallons,  and  the 
average  consumption  about  200,000  gallons  daily. 

The  plant  at  Keyport,  N.  J.,  is  similar,  but  smaller. 


TREATMENT  OF   WATERS. 


CHAPTER    XIII. 
TREATMENT   OF  WATERS. 

HAVING  now  reviewed  the  most  important  methods  in  use  for 
the  treatment  of  waters,  we  may  take  a  general  view  of  their 
application  to  various  classes  of  waters.  Different  raw  waters  vary 
so  much,  and  the  requirements  of  filtration  are  so  different,  that  it 
is  not  possible  to  outline  any  general  procedure  or  combination  of 
procedures,  but  each  problem  must  be  taken  up  by  itself.  Never- 
theless, some  general  suggestions  may  be  of  service. 

In  the  first  place,  we  may  consider  the  case  of  waters  contain- 
ing very  large  quantities  of  oxidizable  organic  matter.  Such 
waters  are  obtained  from  some  reservoirs  containing  very  active 
vegetable  and  animal  growths,  or  from  rivers  receiving  large 
amounts  of  sewage.  Waters  of  both  of  these  classes  are,  if  possi- 
ble, to  be  avoided  for  public  water-supplies.  When  circumstances 
require  their  use,  they  can  best  be  treated  by  intermittent  filtra- 
tion, this  process  being  best  adapted  to  the  destruction  by  oxygen 
of  excessive  quantities  of  organic  matter. 

Where  the  pollution  is  less,  so  that  the  dissolved  oxygen 
contained  in  the  raw  water  is  sufficient  for  the  oxidation  of  the 
organic  matters,  continuous  filtration  will  give  substantially  as 
good  results  as  intermittent  filtration,  and  in  other  respects  it  has 
important  advantages.  The  application  of  intermittent  filtration  for 
the  treatment  of  public  water-supplies  is  thus  somewhat  limited, 
and,  as  a  matter  of  fact,  it  has  been  used  in  only  a  few  cases. 

For  the  treatment  of  very  highly  polluted  waters  double 
filtration  has  been  used  in  a  number  of  cases,  notably  by  the 
Grand  Junction  Company  at  London,  at  Schiedam  in  Holland,  and 
at  Bremen  and  Altona  in  Germany.  At  the  two  first-mentioned 


198  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

places  two  separate  systems  of  filters  are  provided  differing 
somewhat  in  construction,  the  first  filters  being  at  a  higher  level 
than  the  after  filters.  The  first  filters  supply  water  of  comparative 
purity,  and  very  constant  composition,  to  the  after  filters,  which 
.are  able  to  treat  it  with  great  efficiency  and  at  very  low  operating 
cost. 

This  procedure  is  probably  the  most  perfect  which  has  been 
used  for  the  removal  of  disease-producing  qualities  from  highly 
polluted  waters;  and  the  cost  of  the  process  may  not  be  as  much 
greater  than  that  of  simple  filtration  as  would  at  first  appear, 
because  the  cost  of  cleaning  the  after  filters  is  merely  nominal,  and 
the  attendance,  pumping,  etc.,  are  practically  common  to  both 
sets  of  filters,  and  are  not  materially  greater  than  they  would  be  for 
a  single  set. 

For  very  bad  waters  the  first  filters  might  appropriately  be 
intermittent,  while  the  after  filters  should  be  continuous.  This 
was  the  procedure  originally  intended  for  Lawrence,  but  the 
intermittent  filter  first  constructed  yielded  such  very  good  results 
that  it  has  not  been  considered  necessary  to  complete  the  plant 
as  originally  projected. 

At  Bremen  and  at  Altona  a  different  procedure  has  been 
adopted.  The  filters  are  all  upon  the  same  level,  and  of  the  same 
construction.  When  a  filter  is  put  in  service  the  effluent  from  it, 
instead  of  being  taken  to  the  pure-water  reservoir,  is  taken  to 
another  filter  which  has  already  been  some  time  in  service.  After 
the  first  filter  has  been  in  operation  for  some  time  its  effluent  is 
tiken  to  the  pure-water  reservoir,  and  in  turn  it  is  supplied  with 
the  effluent  from  a  filter  more  recently  cleaned.  The  loss  of  head 
of  water  passing  a  freshly  cleaned  filter  is  comparatively  slight,  and 
the  water  of  the  second  filter  is  allowed  to  fall  a  few  inches  below 
the  high-water  mark,  at  which  level  it  will  take  the  effluent  from 
the  other  filter.  The  connections  between  the  filters  are  made  by 
siphons  of  large  pipe,  the  summits  of  which  are  considerably  above 
the  high-water  line.  These  siphons  are  ftPed  by  exhausting  the 


TREATMENT  OF   WATERS.  1 99 

air,  and  when  opened  to  the  air  there  is  no  possibility  of  a  flow  of 
water  through  them.  The  process  has  given  extremely  good 
results  in  practice,  yielding  effluents  of  the  very  greatest  purity 
and  at  a  quite  moderate  cost  of  operation. 

An  objection  to  the  method  is  the  possible  filling  of  a  siphon 
some  time  when  the  water  standing  upon  the  after-filter  is  higher 
than  that  in  the  pure-water  well  of  the  fore-filter,  and  while  the 
fore-filter  is  connected  with  the  pure-water  reservoir.  Such  a 
connection  would  send  unfiltered  water  into  the  pure-water  reser- 
voir direct.  I  do  not  know  that  any  trouble  of  this  kind  has  ever 
been  experienced  at  Bremen  or  at  Altona;  and  the  objection  tb 
this  system  is  perhaps  not  well  founded  where  the  management  is 
careful  and  conscientious.  The  fact  that  an  unscrupulous  attend- 
ant can  make  the  connection  at  any  time  to  help  out  a  deficiency 
of  supply,  or  simply  through  carelessness,  is  certainly  objection- 
able. 

For  the  treatment  of  river-waters  and  lake-waters  containing 
only  a  small  quantity  of  sediment,  and  where  the  removal  of 
bacteria  or  disease-producing  qualities  is  the  most  important 
object  of  filtration,  sand  filters  can  be  used.  Where  the  rivers  are 
subject  to  floods  and  moderate  amounts  of  muddy  water,  sedi- 
mentation-basins or  storage  reservoirs  for  raw  water  will  often  be 
found  advantageous. 

For  the  treatment  of  extremely  muddy  waters,  and  waters 
which  are  continuously  muddy  for  long  periods  of  time,  and  for 
the  removal  of  color  from  very  highly  colored  waters,  resource 
must  be  had  to  coagulants.  The  coagulants  which  are  necessary 
in  each  special  case  and  which  can  be  used  without  injury  to  the 
water  must  be  determined  by  most  careful  investigation  of  the 
raw  water. 

For  the  filtration  of  these  waters  after  coagulation  either  sand 
or  mechanical  filters  can  be  employed.  As  the  principal  work  in 
this  case  is  done  by  the  coagulant,  the  kind  of  filtration  employed 
is  of  less  consequence  than  where  filtration  alone  is  relied  upon, 


2OO  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

and  the  cheapest  form  of  filter  will  naturally  be  employed. 
Under  present  conditions  mechanical  filters  will  usually  be  cheaper 
than  sand  filters  for  use  in  this  way;  but  where  waters,  in  addition 
to  the,  mud,  carry  bacteria  in  such  large  numbers  as  to  make  high 
bacterial  efficiency  a  matter  of  importance,  sand  filters  may  be 
selected,  as  the  bacterial  efficiency  obtained  with  them  is  not 
dependent  upon  the  use  of  coagulant;  and  is  therefore  less  subject 
to  interruptions  from  the  failure  to  apply  coagulant  in  the  right 
proportion. 

Mechanical  filters  have  also  been  used  for  the  treatment  of 
comparatively  clear  waters  where  bacterial  efficiency  was  the  prin- 
cipal object  of  filtration.  For  this  purpose  the  efficiencies  obtained 
with  them  are  usually  inferior  to  those  obtained  with  sand  filters, 
fvhile  the  cost  of  coagulants  is  so  great  as  to  make  their  use  often 
more  expensive  than  that  of  sand  filters. 

In  the  case  of  many  streams  which  are  comparatively  clear  for 
a  part  of  the  year,  but  occasionally  are  quite  turbid,  the  use  of 
sand  filters  has  this  advantage,  that  the  use  of  coagulants  can  be 
stopped  and  the  cost  of  operation  reduced  whenever  the  water  is 
clear  enough  to  allow  of  satisfactory  treatment  by  them ;  and  that 
coagulant  can  be  employed  on  those  days  when  otherwise  insuffi- 
cient clarification  would  be  obtained. 

In  this  case  the  high  bacterial  efficiency  is  secured  at  all  times, 
while  the  cost  of  coagulant  is  saved  during  the  greater  part  of  the 
time.  In  such  cases,  also,  the  preliminary  process  of  sedimenta- 
tion and  storage  should  be  developed  as  far  as  possible. 

The  application  of  other  processes  of  filtration  to  special 
problems  are  not  sufficiently  well  understood  to  allow  general  dis- 
cussion, and  must  be  taken  up  separately  with  reference  to  the 
requirements  of  each  special  situation. 

COST   OF   FILTRATION. 

The  cost  of  filtration  of  water  depends  upon  the  character  of 
the  raw  water,  upon  the  nature  of  the  plant  employed,  upon  its 


TREATMENT  OF   WATERS.  2OI 

size,  and  upon  the  skill  and  economy  of  manipulation.  These 
conditions  affect  the  cost  to  such  an  extent  as  to  make  any 
accurate  general  estimate  quite  impossible.  Nevertheless  a  little 
consideration  of  the  subject,  although  not  leading  to  exact  results, 
may  be  helpful  as  furnishing  a  rough  idea  of  the  probable  cost 
before  estimates  for  local  conditions  are  made. 

Open  sand  filters,  with  masonry  walls,  with  reasonably  favor- 
able conditions  of  construction,  and  not  too  small  in  area,  have 
averaged  to  cost  in  the  United  States  within  the  last  few  years 
perhaps  about  thirty  thousand  dollars  per  acre.  The  relative  cost 
of  small  plants  is  somewhat  greater,  and  with  embankments 
instead  of  masonry  walls,  the  cost  is  somewhat  reduced.  The  cost 
is  less  where  natural  deposits  of  sand  can  be  made  use  of  practically 
in  their  original  condition,  and  is  increased  where  the  filtering 
materials  have  to  be  transported  by  rail  for  long  distances,  or  where 
the  sites  are  difficult  to  build  upon.  Covered  filters  cost  about  a 
half  more  than  open  filters.  Mechanical  filters  at  current  prices 
cost  about  §20  per  square  foot  of  filtering  area,  to  which  must  be 
added  the  cost  of  foundations  and  buildings,  which  perhaps  average 
to  cost  half  as  much  more,  but  are  dependent  upon  local  condi- 
tions and  the  character  of  the  buildings. 

To  these  figures  must  be  added  the  costs  of  pumps,  reservoirs, 
sedimentation-basins,  and  pipe-connections,  which  are  often 
greater  than  the  costs  of  the  filters,  but  which  differ  so  widely  in 
different  cases  as  to  make  any  general  estimate  impossible. 

Filters  must  be  provided  sufficient  to  meet  the  maximum  and 
not  the  average  consumption.  The  excess  of  maximum  over 
average  requirements  varies  greatly  in  different  cities,  and  depends 
largely  upon  reservoir  capacities  and  arrangements. 

As  a  result  of  a  considerable  number  of  estimates  made  by  the 
author  for  average  American  conditions,  the  cost  of  installing 
filters  may  be  taken  very  roughly  as  five  dollars  per  inhabitant, 
but  the  amounts  differ  widely  in  various  cases. 

The   cost   of   operation    of    sand   filters  in   England    probably 


202 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


averages  about  one  dollar  per  million  gallons  of  water  filtered. 
The  following  table  shows  the  costs  of  operation  of  the  filters  of 
the  seven  London  companies  for  fifteen  years,  compiled  in  the 
office  of  Mr.  W.  B.  Bryan,  Chief  Engineer  of  the  East  London 
Water  Company.  The  results  have  been  computed  to  dollars  per 
million  U.  S.  gallons,  and  include  the  cost  of  all  labor,  sand,  and 
supplies  for  the  filters,  but  do  not  include  any  pumping  or  interest 
costs. 

COST   OF    FILTRATION,    LONDON    WATER   COMPANIES. 
(Computed  from  data  furnished  Wm.  B.  Bryan,  C.E.,  East  London  Water  Works.) 
Dollars  per  Million  U.  S.  Gallons. 


South- 

Chelsea 
Co. 

East 
London 
Co. 

Grand 
Junction 
Co. 

Lambeth 
Co. 

New 

River 
Co. 

wark 
& 
Vauxhall 

West 
Middle- 
sex Co. 

Average. 

Co. 

1880-1 

.16 

.16 

I.  00 

0.83 

•34 

.16 

1.67 

.IQ 

1881-2 

.19 

•  39 

0.95 

0.82 

•15 

•37 

•54 

.20 

1882-3 

.10 

•23 

•39 

0.96 

.40 

•47 

•74 

•33 

1883-4 

.00 

.06 

•73 

0.92 

.11 

.62 

.67 

•30 

1884-5 

.06 

.06 

.82 

0.90 

.02 

.40 

•30 

.22 

1885-6 

.15 

.16 

•35 

0.90 

.OO 

•15 

.07 

.  II 

1886-7 

0.80 

.96 

•39 

0.87 

0.98 

•43 

.70 

.16 

1887-8 

1.07 

.22 

•74 

0.90 

0.92 

.28 

1.  00 

.16 

1888-9 

0.83 

.28 

•55 

0-95 

0.98 

•52 

0.83 

•13 

1889-90 

0.66 

•50 

.22 

0.88 

0.90 

.70 

3-56 

•49 

1890-1 

0.72 

-42 

•32 

0.85 

I.  O2 

.16 

I.OO 

.07 

1891-2 

0-75 

•54 

•23 

I.  00 

0.92 

•15 

0.96 

.08 

1892-3 

0.67 

.42 

•30 

1.19 

1.16 

.26 

1.42 

.20 

1893-4 

I-  15 

2.63 

2.OO 

1.46 

1-43 

•52 

0.95 

•59 

1894-5 

0.60 

1.68 

1.67 

2.53 

1.03 

•34 

0.96 

.40 

Average.  .  .  . 

o-93 

1.38 

1.44 

i.  06 

1.09 

i-37 

i-43 

1.24 

Average  of  seven  companies  for  15  years,  $1.24  per  million  gallons. 

Variations  from  year  to  year  are  caused  by  differences  in  the  amounts  of  ice, 
and  in  the  quantities  of  new  sand  purchased.  Wages  average  about  $1.00  per 
day.  At  Liverpool  for  1896  the  cost  was  $1.08  per  million  U.  S.  gallons. 

In  Germany,  with  more  turbid  river-waters,  the  costs  of  opera- 
tion are  somewhat  higher  than  the  London  figures,  while  at 
Zurich,  where  the  water  is  very  clear,  they  are  lower. 

In  the  United  States  the  data  regarding  the  cost  of  operation 
of  sand  filters  are  less  complete.  At  Mt.  Vernon,  N.  Y.,  with 


TREATMENT  OF   WATERS.  203 

reservoir-water,  the  cost  has  averaged  about  two  dollars  per  million 
gallons.  At  Poughkeepsie,  N.  Y.,  with  the  Hudson  River  water, 
which  is  occasionally  moderately  turbid,  the  cost  for  twenty 
years  has  averaged  three  dollars  per  million  gallons.  This  cost 
includes  the  cost  of  handling  ice,  and  as  the  average  winter  tem- 
perature is  considerably  below  that  suggested  for  open  filters,  the 
expense  of  this  work  has  been  considerable,  and  has  increased 
considerably  the  total  cost  of  operation. 

At  Far  Rockaway,  L.  I.,  and  Red  Bank  N.  J.,  for  iron- 
removal  plants,  the  cost  of  operation  has  hardly  been  appreciable. 
The  plants  are  both  close  to  the  pumping-stations,  and  it  has  been 
possible  to  operate  them  with  the  labor  necessarily  engaged  at  the 
pumping-station  without  additional  cost,  except  a  very  small 
amount  of  labor  on  the  sand  at  Far  Rockaway.  No  computation 
has  been  made  in  these  cases  of  the  additional  coal  required  for 
pumping. 

At  Lawrence,  Mass.,  the  cost  of  operation  for  1895  was  as 
follows : 

Cost  of  scraping  and  replacing  sand $3,467 

Cost  of  care  of  ice 2,903 


Total  cost  of  operation $6,370 

Water  filtered,  millions  of  gallons I>°97 

Cost  per  million  gallons $5.80 

The  cost  of  care  of  ice  has  been  excessive  at  Lawrence,  and  it 
has  been  repeatedly  recommended  to  cover  the  filter  to  avoid 
this  expense.  The  cost  of  handling  sand  has  been  very  greatly 
increased,  because  the  filter  is  built  in  one  bed,  and  all  work  upon 
it  has  to  be  done  during  the  comparatively  short  intervals  when 
the  filter  is  not  in  use,  an  arrangement  which  is  not  at  all  economi- 
cal in  the  use  of  labor.  The  cost  of  operation  is  thus  much  higher 
than  it  would  be  had  the  plant  been  constructed  in  several  units, 
each  of  which  could  be  disconnected  for  the  purpose  of  being 
cleaned  in  the  ordinary  manner.  As  against  this  the  first  cost 


204  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

of  construction  was  extremely  low,  and  the  saving  in  interest 
charges  should  be  credited  against  the  increased  cost  of  labor  in 
cleaning. 

The  cost  of  operating  filters  at  Ashland,  Wis.,  has  been 
estimated  by  Mr.  William  Wheeler  at  $2.26  per  million  gallons. 
This  estimate  is  based  upon  the  performance  for  the  first  year  that 
they  were  in  service. 

In  the  operation  of  mechanical  filters  one  of  the  largest  items 
of  expense  is  for  the  coagulant,  and  the  amount  of  this  depends 
entirely  upon  the  character  of  the  raw  water  and  the  thoroughness 
of  the  treatment  required.  The  data  regarding  the  other  or 
general  costs  of  operation  of  mechanical  filters  are  few  and  unsatis- 
factory. 

I  recently  made  some  estimates  of  cost  of  clarifying  waters 
of  various  degrees  of  turbidity  by  sand  and  mechanical  filters. 
These  estimates  were  made  for  a  special  set  of  conditions,  and  I 
do  not  know  that  they  will  fit  others,  but  they  have  at  least  a 
suggestive  value.  The  results  shown  by  Fig.  26  include  only 
the  cost  of  operation,  and  not  interest  and  depreciation  charges. 
These  figures,  when  used  for  plants  in  connection  with  which 
preliminary  treatments  are  used,  should  be  applied  to  the  tur- 
bidity of  the  water  as  applied  to  the  filters,  and  not  to  the 
raw  water,  and  the  costs  of  the  preliminary  processes  should  be 
added. 

With  sand  filters  the  frequency  of  scraping  is  nearly  propor- 
tional to  the  turbidity;  and  as  scraping  represents  most  of  the 
expenses,  the  costs  of  operation  are  proportional  to  the  turbidity, 
except  the  general  costs,  and  the  cost  of  the  amount  of  scraping, 
which  is  necessary  with  even  the  clearest  waters. 

With  mechanical  filters  the  amount  of  sulphate  of  alumina 
required  for  clarification  increases  with  the  turbidity,  and  most  of 
the  costs  of  operation  increase  in  the  same  ratio.  The  diagram 
shows  the  amount  of  sulphate  of  alumina  in  grains  per  galloa 
necessary  for  clarification  with  different  degrees  of  turbidity. 


TREATMENT  OF    WATERS. 


205 


With  the  clearest  waters  the  costs  of  operation  on  the  two 
systems  are  substantially  equal.  With  muddy  waters,  the  expense 
of  operating  sand  filters  increases  more  rapidly  than  the  expense 
of  operating  mechanical  filters. 


8 


CO 

6 


CO 

cc 


o 

Q 


ZZ3 


'0 


FOR  98, 


ON  EG 


1A/N  PER/GALLON . 


CY 


8 


000          0.10          0.20          030         0.40         0.50          0.60         0.70 

TURBIDITY 

FIG,  26. — COST  OF  OPERATION  OF  FILTERS. 

There  is  another  element  which  often  comes  into  the  compari- 
son, namely,  the  question  of  purification  from  the  effects  of 
sewage-pollution.  Nearly  all  rivers  used  for  public  water-supplies 


206  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

receive  more  or  less  sewage,  and  in  filtering  such  waters  it  is 
regarded  as  necessary  to  remove  as  completely  as  possible  the 
bacteria. 

The  quantities  of  sulphate  of  alumina  required  for  the  clarifica- 
tion of  the  least  turbid  waters  are  not  sufficient  to  give  even 
tolerably  good  bacterial  efficiencies.  To  secure  a  reasonably  com- 
plete removal  of  bacteria  with  mechanical  filters,  the  use  of  a 
considerable  quantity  of  sulphate  of  alumina  is  required.  Let  us 
assume  that  98  per  cent  bacterial  efficiency  is  required,  and  that 
to  produce  this  efficiency  it  is  necessary  to  use  one  grain  of 
coagulant  to  the  gallon.  With  water  requiring  less  than  this 
quantity  of  coagulant  for  clarification  this  quantity  must  neverthe- 
less be  used,  and  the  costs  will  be  controlled  by  it,  and  not  by 
the  lower  quantities  which  would  suffice  for  clarification,  but 
would  not  give  the  required  bacterial  efficiency. 

I  have  added  this  line  to  the  diagram,  and  this,  com- 
bined with  the  upper  portion  of  the  line  showing  cost  of  clarifica- 
tion, represents  the  cost  of  treating  waters  with  mechanical 
filters,  where  both  bacterial  efficiency  and  clarification  are  re- 
quired. 

This  line,  considered  as  a  whole,  increases  much  less  rapidly 
with  increasing  turbidity  than  does  the  corresponding  line  for  sand 
filters,  and  the  two  lines  cross  each  other.  With  the  clearest 
waters  sand  filters  are  cheaper  than  mechanical  filters,  and  for  the 
muddiest  waters  they  are  more  expensive.  It  does  not  appear 
from  the  diagram,  but  it  is  also  true  in  each  case,  that  the  cheaper 
system  is  also  the  more  efficient.  Sand  filters  are  more  efficient 
in  removing  bacteria  from  clear  waters  than  are  mechanical  filters, 
and  mechanical  filters  are  more  efficient  in  clarifying  very  muddy 
waters  than  are  sand  filters. 


TREATMENT  OF    WATERS.  2O? 

WHAT  WATERS   REQUIRE  FILTRATION? 

From  the  nature  of  the  case  a  satisfactory  general  answer  to 
this  question  cannot  be  given,  but  a  few  suggestions  may  be  useful. 

In  the  first  place,  ground-waters  obviously  do  not  require  filtra- 
tion :  they  have  already  in  most  cases  been  thoroughly  filtered  in 
the  ground  through  which  they  have  passed,  and  in  the  exceptional 
cases,  as,  for  instance,  an  artesian  well  drawing  water  through  fis- 
sures in  a  ledge  from  a  polluted  origin,  a  new  supply  will  generally 
be  chosen  rather  than  to  attempt  to  improve  so  doubtful  a  raw 
material. 

River-waters  should  be  filtered.  It  cannot  be  asserted  that 
there  are  no  rivers  in  montainous  districts  in  which  the  water  is  at 
once  clear  and  free  from  pollution,  and  suitable  in  its  natural  state 
for  water-supply;  but  if  so,  they  are  not  common,  least  of  all  in  the 
regions  where  water-supplies  are  usually  required.  The  use  of 
river-waters  in  their  natural  state  or  after  sedimentation  only, 
drawn  from  such  rivers  as  the  Merrimac,  Hudson,  Potomac,  Dela- 
ware, Schuylkill,  Ohio,  and  Mississippi,  is  a  filthy  as  well  as  an 
unhealthy  practice,  which  ought  to  be  abandoned. 

The  question  is  more  difficult  in  the  case  of  supplies  drawn  from 
lakes  or  storage  reservoirs.  Many  such  supplies  are  grossly  polluted 
and  should  be  either  abandoned  or  filtered.  Others  are  subject  to 
algae  growths,  or  are  muddy,  and  would  be  much  improved  by  fil- 
tration. Still  others  are  drawn  either  from  unpolluted  water-sheds, 
or  the  pollution  is  so  greatly  diluted  and  reduced  by  storage  that 
no  known  disadvantage  results  from  their  use. 

In  measuring  the  effects  of  the  pollution  of  water-supplies,  the 
typhoid-fever  death-rate  is  a  most  important  aid.  Not  that  typhoid 
fever  is  the  sole  evil  resulting  from  polluted  water,  but  because  it 
is  also  a  very  useful  index  of  other  evils  for  which  corresponding 
statistics  cannot  be  obtained,  as,  for  instance,  the  causation  of 
diarrhoeal  diseases  or  the  danger  from  invasion  by  cholera. 


2O8  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

I  think  we  shall  not  go  far  wrong  at  the  start  to  confine  our 
attention  to  those  cities  where  there  are  over  25  deaths  from 
typhoid  fever  per  100,000  of  population.  This  will  at  once  throw 
out  of  consideration  a  large  number  of  relatively  good  supplies,  in- 
cluding those  of  New  York  and  Brooklyn.  It  is  not  my  idea  that 
none  of  these  supplies  cause  disease.  Many  of  them,  as  for  instance 
that  of  New  York,  are  known  to  receive  sewage,  and  it  is  an  in- 
teresting question  worthy  of  most  careful  study  whether  there  are 
cases  of  sickness  resulting  from  this  pollution.  The  point  that  I 
wish  to  make  now  is  simply  that  in  those  cases  the  death-rate  itself 
is  evidence  that,  with  existing  conditions  of  dilution  and  storage, 
the  resulting  damage  of  which  we  have  knowledge  is  not  great 
enough  to  justify  the  expense  involved  by  filtration. 

In  this  connection  it  should  not  be  forgotten  that,  especially 
with  very  small  watersheds,  there  may  be  a  danger  as  distinct  from 
present  damage  which  requires  consideration.  Thus  a  single  house 
or  groups  of  houses  draining  into  a  supply  may  not  appreciably 
affect  it  for  years,  until  an  outbreak  of  fever  on  the  water-shed 
results  in  infecting  the  water  with  the  germs  of  disease  and  in 
an  epidemic  in  the  city  below.  This  danger  decreases  with  in- 
creasing size  of  the  water-shed  and  volume  of  the  water  with  which 
any  such  pollution  would  be  mixed,  and  also  with  the  population 
draining  into  the  water,  as  there  is  a  probability  that  the  amount 
of  infection  continually  added  from  a  considerable  town  will  not 
be  subject  to  as  violent  fluctuation  as  that  from  only  a  few  houses. 

Thus  in  Plymouth,  Pa.,  in  1885,  there  were  1104  cases  of  typhoid 
fever  and  114  deaths  among  a  population  of  8000,  as  the  result  of 
the  discharge  of  the  dejecta  from  a  single  typhoid  patient  into  the 
water  of  a  relatively  small  impounding  reservoir.  The  cost  of  this 
epidemic  was  calculated  with  unusual  care.  The  care  of  the  sick 
cost  in  cash  $67,100.17,  and  the  loss  of  wages  for  those  who  recovered 
amounted  to  $30,020.08.  The  1 14  persons  who  died  were  earning 
before  their  sickness  at  the  rate  of  $18,419.52  annually. 

Such  an  outbreak  would   hardly  be  possible  with    the    Croton 


TREATMENT  OF   WATERS.  2OQ 

water-shed  of  the  New  York  water-supply,  on  account  of  the  great 
dilution  and  delay  in  the  reservoirs,  but  it  must  be  guarded  against 
in  small  supplies. 

Of  the  cities  having  more  than  25  deaths  per  100,000  from  typhoid 
fever,  some  will  no  doubt  be  found  where  milk  epidemics  or  other 
special  circumstances  were  the  cause ;  but  I  believe  in  a  majority  of 
them,  and  in  nearly  all  cases  where  the  rate  is  year  after  year  con- 
siderably above  that  figure,  the  cause  will  be  found  in  the  water-sup- 
ply. Investigation  should  be  made  of  this  point ;  and  if  the  water 
is  not  at  fault,  the  responsibility  should  be  located.  If  the  water  is 
guilty,  it  should  be  either  purified  or  a  new  supply  obtained. 


2IO  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


CHAPTER    XIV. 
WATER-SUPPLY   AND   DISEASE— CONCLUSIONS. 

ONE  of  the  most  characteristic  and  uniform  results  of  the 
direct  pollution  of  public  water-supplies  is  the  typhoid  fever  which 
results  among  the  users  of  the  water.  In  the  English  and  German 
cities  with  almost  uniformly  good  drinking-water,  typhoid  fever  is 
already  nearly  exterminated,  and  is  decreasing  from  year  to  year. 
American  cities  having  unpolluted  water-supplies  have  compara- 
tively few  deaths  from  this  cause,  although  the  figures  never  go 
so  low  as  in  Europe,  perhaps  on  account  of  the  fresh  cases  which 
are  always  coming  in  from  less  healthy  neighborhoods  in  ever- 
moving  American  communities.  In  other  American  cities  the 
death-rates  from  typhoid  fever  are  many  times  what  they  ought 
to  be  and  what  they  actually  are  in  other  cities,  and  the  rates  in 
various  places,  and  in  the  same  place  at  different  times,  bear  in 
general  a  close  relation  to  the  extent  of  the  pollution  of  the 
drinking-water.  The  power  of  suitable  filtration  to  protect  a  city 
from  typhoid  fever  is  amply  shown  by  the  very  low  death-rates 
from  this  cause  in  London,  Berlin,  Breslau,  and  large  numbers  of 
other  cities  drawing  their  raw  water  from  sources  more  contami- 
nated than  those  of  any  but  the  very  worst  American  supplies, 
and  by  the  marked  and  great  reductions  in  the  typhoid-fever 
death  rates  which  have  followed  at  once  the  installation  of  niters 
at  Zurich,  Switzerland;  Hamburg,  Germany;  Lawrence,  Mass., 
and  other  places. 

The  following  is  a  list  of  the  cities  of  50,000  inhabitants  and  up- 


WATER-SUPPLY  AND    DISEASE— CONCLUSIONS. 


2IP 


ward  in  the  United  States,  with  deaths  from  typhoid  fever  and  the 
sources  of  their  water-supplies.  The  deaths  and  populations  are  from 
the  U.  S.  Census  for  1890;  the  sources  of  the  water-supplies,  from 
the  American  Water-Works  Manual  for  the  same  year.  Four  cities 
of  this  size — Grand  Rapids,  Lincoln,  St.  Joseph,  and  Des  Moines— 
are  not  included  in  the  census  returns  of  mortality.  Two  cities 
with  less  than  50,000  inhabitants  with  exceptionally  high  death- 
rates  have  been  included,  and  at  the  foot  of  the  list  are  given  cor- 
responding data  for  some  large  European  cities  for  1893. 
TYPHOID  FEVER  DEATH-RATES  AND  WATER-SUPPLIES  OF  CITIES. 


City. 

Population. 

Deaths  from 
Typhoid 
Fever. 

Water-supply. 

Total. 

Per 

IOO.OOO 

living. 

Birmingham... 
i    Denver  

26,178 
106,713 
105,287 

58.313 
238,617 

44,654 
181,830 

54,955 
230,392 

77,696 
163,003 
161,129 
i  ,046,964 
1,099,850 
65,533 
94,923 
6i,43J 

'P'5^ 
60,956 

50,395 
76,168 
261,353 
81,388 
53,230 
74,398 
164,738 
298,997 
105,436 
296,908 

64,495 
58,661 

434,439 

69 
232 
I92 

77 
3°4 

,£ 

54 

200 
64 
134 
122 

770 

794 
47 
67 
43 
92 
42 
34 
49 
164 
50 
32 
44 
94 
166 

57 
151 
33 
29 

202 

264 
217 
182 
132 
127 
121 
100 
98 
87 
82 
82 
76 

74 
72 
72 
7i 
70 

69 
69 

67 

64 
63 
61 
60 
59 

11 

54 
5i 
5i 
49 
47 

Five  Mile  Creek 
North  Platte  River  and  wells 
Allegheny  River 
Delaware  River 
Allegheny  and  Monongahela  rivers 
Merrimac  River 
Passaic  River                        [Ions  daily 
Artesian  wells  yielding  1,600,000  gal- 
Potomac  River 
Merrimac  River 
Passaic  River 
Ohio  River 
Delaware  and  Schuylkill  rivers 
Lake  Michigan 
South  River 
Hudson  River 
Brandywine  Creek 
Lakes              ,                           [ervoirs 
Hudson  River  and  impounding  res- 
Los  Angeles  River  and  springs 
Cumberland  River 
Lake  Erie 
James  River                           [reservoir 
Connecticut  River  and  impounding 
Watupa  Lake 
Mississippi  River 
Lobus     Creek,    Lake    Merced,    and 
White  River           [mountain  streams 
Ohio  River 
Artesian  Wells 
Maiden  Creek  and  Springs 
Impounding  reservoir 

2.  Allegheny.  .  .. 

j.    Pittsburgh  .  . 

Lawrence  
5    Newark  .... 

6.  Charleston  
7.  Washington... 
8    Lowell 

9.  Jersey  City.  .  . 
10.  Louisville  .... 
u.  Philadelphia.. 
12    Chicago 

13    Atlanta  .... 

14.  Albany  

15.  Wilmington.  . 
16    St   Paul   ...   . 

1  8.  Los  Angeles.. 
19.  Nashville  
20.  Cleveland  
21.  Richmond  
22.  Hartford  
23.  Fall  River  
24.  Minneapolis.  . 
25.  San  Francisco 
26.  Indianapolis.. 
27.  Cincinnati 
28.  Memphis  
29.  Reading  

30.  Baltimore  

212 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


TYPHOID    FEVER    DEATH-RATES    AND    WATER-SUPPLIES    OF    CITIES. 


City. 

Population. 

Deaths  from 
Typhoid 
Fever. 

Water-supply. 

Total  . 

Per 

100,000 
living. 

31    Omaha 

140,452 
88,150 
132,146 
132,716 
133,896 
50,756 
448,477 
81,434 
70,028 

45I.770 
75.215 
255,664 
204,468 
81,298 
84,655 

78,347 
6l,220 

806,343 

['588J43 
242,039 
205,876 

55.727 
57458 

4,306,411 
667,883 
2,424,705 
437,892 
222,233 
169,828 
1,714,938 
634,878 

353.551 
308,930 
I.435.93I 

63 
38 

53 
53 
53 

20 

174 
29 

24 
145 
24 
80 

61 

22 
22 
20 

15 
194 

348 

18 

45 
40 

9 
9 

719 
138 
609 
69 

16? 

37 
H 
104 

45 
43 
40 
40 
39 
39 
39 
36 
34 
32 
32 

30 
27 
26 
26 

25 
24 

23 

20 
19 
19 

16 
16 

17 

20 

3 

5 

J 

ii 

5 
7 

Missouri  River 
Surface-water  and  wells 
Pawtuxet  River 
Missouri  River 
Hemlock  and  Candice  lakes 
Ohio  River 
Impounding  reservoirs 
Maumee  River 
Impounding  reservoir 
Mississippi  River 
Impounding   reservoir 
Niagara  River 
Lake  Michigan 
Impounding  reservoir 
Impounding  reservoir 
Passaic  River  (higher  up) 
Wells                                         [ervoirs 
Wells,  ponds,  and  impounding  res- 
Impounding  reservoir 
Impounding  reservoir  and  springs 
Mississippi  River 
Detroit  River 
Impounding  reservoir 
Delaware  River 

Filtered  Thames  and  Lea  rivers  and 
Loch  Katrine                  [£  from  wells 
Spring  water 
Filtered  dune-water 
Filtered  Maas  River 
Filtered  dune-water 
Filtered  Havel  and  Spree  rivers 
Filtered  Elbe  River 
Filtered  Oder  River 
Ground-water 
Spring-water 

32.  Columbus.  .  .  . 
33.  Providence.  .  . 
34.  Kansas  City.  . 
35.  Rochester  
36.  Evansville  
37    Boston 

38.  Toledo 

39.  Cambridge  ... 
40.  St.  Louis  
41    Scranton 

42    Buffalo 

43.  Milwaukee.  ... 
44.  New  Haven. 
45.  Worcester.  .  .. 
46.  Paterson   .    . 

47    Dayton 

48.  Brooklyn.  .  .  . 
49.  New  York  
50.  Syracuse...  .  . 
51.  New  Orleans.. 
52.  Detroit  ...     .  . 
53.  Lynn     .     ... 

54.  Trenton 

Glasgow  
Paris  

Amsterdam  .  . 
Rotterdam  — 
Hague 

Berlin 

Hamburg  
Breslau  

Dresden  
Vienna  

Any  full  discussion  of  these  data  would  require  intimate  aquaint- 
ances  with  the  various  local  conditions  which  it  is  impossible  to 
take  up  in  detail  here,  but  some  of  the  leading  facts  cannot  fail  to 
be  instructive. 

Each  of  the  places  having  over  100  deaths  per  100,000  from 
typhoid  fever  used  unfiltered  river-water.  Lower  in  the  list,  but 


IV A  TER-SUrn.  \ '   A  XD    DISEA  SE—CONCL  US  JONS.  2  1 3 

still  very  high,  Charleston,  said  to  have  been  supplied  only  from 
artesian  wells,  had  an  excessive  rate;  but  the  reported  water-con- 
sumption is  so  low  as  to  suggest  that  private  wells  or  other  means 
of  supply  were  in  common  use.  Chicago  and  Cleveland  both  drew 
their  water  from  lakes  where  they  were  contaminated  by  their  own 
sewage.  St.  Paul's  supply  came  from  ponds,  of  which  I  do  not 
know  the  character.  With  these  exceptions  all  of  the  22  cities 
with  over  50,000  inhabitants,  at  the  head  of  the  list,  had  unfiltered 
river-water. 

The  cities  supplied  from  impounding  reservoirs  as  a  rule  had 
lower  death  rates  and  are  at  the  lower  end  of  the  list,  together  with 
some  cities  taking  their  water  supplies  from  rivers  or  lakes  at 
points  where  they  were  subject  to  only  smaller  or  more  remote 
infection.  Only  three  of  the  American  cities  in  the  list  were  re- 
ported as  being  supplied  entirely  with  ground-water. 

It  is  not  my  purpose  to  make  too  close  comparisons  between  the 
various  cities  on  the  list ;  some  of  them  may  have  been  influenced 
by  unusual  local  conditions  in  1890.  Others  have  in  one  way  or 
another  improved  their  water-supplies  since  that  date,  and  there  are 
several  cities  in  which  I  know  the  present  typhoid-fever  death- 
rates  to  be  materially  lower  than  those  of  1890  given  in  the 
table.  On  the  other  hand,  it  is  equally  true  that  a  number  of  cities, 
including  some  of  the  larger  ones,  have  since  had  severe  epidemics 
of  typhoid  fever  which  have  given  very  much  higher  rates  than 
those  for  1890. 

These  fluctuations  would  change  the  order  of  cities  in  the  list 
from  year  to  year ;  they  would  not  change  the  general  facts,  which 
are  as  true  to-day  as  they  were  in  1890.  Nearly  all  of  the  great 
cities  of  the  United  States  are  supplied  with  unfiltered  surface- 
waters,  and  a  great  majority  of  the  waters  are  taken  from  rivers  and 
lakes  at  points  where  they  are  polluted  by  sewage.  The  death-rates 
from  typhoid  fever  in  those  cities,  whether  they  are  compared  with 
better  supplied  cities  of  this  country,  or  with  European  cities,  are 
enormously  high. 


214  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

Such  rates  were  formerly  common  in  European  cities,  but  they 
have  disappeared  with  better  sanitary  conditions.  The  introduction 
of  filters  has  often  worked  marvellous  changes  in  Europe,  and  in 
Lawrence  the  improvement  in  the  city's  health  with  filtered  water 
was  prompt  and  unquestionable.  There  is  every  reason  to  believe 
that  the  general  introduction  of  better  water  in  American  cities 
will  work  corresponding  revolutions ;  and  looking  at  it  from  a 
merely  money  standpoint,  the  value  of  the  lives  and  the  saving  of 
the  expenses  of  sickness  will  pay  handsomely  when  compared  with 
the  cost  of  good  water. 

The  reasons  for  believing  that  cholera  is  caused  by  polluted 
water  are  entirely  similar  to  those  in  the  case  of  typhoid  fever. 
It  was  no  accident  that  the  epidemic  of  cholera  which  caused  the 
death  of  3400  persons  followed  the  temporary  supply  of  unfiltered 
water  by  the  East  London  Water  Company  in  1866,  while  the 
rest  of  London  remained  nearly  free,  or  that  the  only  serious  out- 
break of  cholera  in  Western  Europe  in  1892  was  at  Hamburg, 
which  was  also  the  only  city  in  Germany  which  used  raw  river- 
water.  This  latter  caused  the  sickness  of  20,000  and  the  death  of 
over  8000  people  within  a  month,  and  an  amount  of  suffering  and 
financial  loss,  with  the  panics  which  resulted,  that  cannot  be 
estimated,  but  that  exceeded  many  times  the*  cost  of  the  filters 
which  have  since  been  put  in  operation.  Hamburg  had  several 
times  before  suffered  severely  from  cholera,  and  the  removal  of 
this  danger  was  a  leading,  although  not  the  sole,  motive  for  the 
construction  of  filters. 

How  little  cities  supplied  with  pure  water  have  to  dread  from 
cholera  is  shown  by  the  experience  of  Altona  and  other  suburbs  of 
Hamburg  with  good  water-supplies,  which  had  but  few  cases  of 
cholera  not  directly  brought  from  the  latter  place,  and  by  the  ex- 
perience of  England,  which  maintained  uninterrupted  commercial 
intercourse  with  the  plague-stricken  city,  absolutely  without  quaran- 
tine, and,  notwithstanding  a  few  cases  which  were  directly  imported, 
the  disease  gained  no  foothold  in  England. 


WATER-SUPPLY  AND    DISEASE— CONCLUSIONS.  215 

I  do  not  know  of  a  single  modern  European  instance  where  a 
city  with  a  good  water-supply  not  directly  infected  by  sewage  has 
suffered  severely  from  cholera.  I  shall  leave  to  others  more 
familiar  with  the  facts  the  discussion  of  what  happened  before  the 
introduction  of  modern  sanitary  methods,  as  well  as  of  the  present 
conditions  in  Asia;  although  I  believe  that  in  these  cases  also 
there  is  plenty  of  evidence  as  to  the  part  water  plays  in  the  spread 
of  the  disease. 

A  considerable  proportion  of  the  water-supplies  of  the  cities  of 
the  United  States  are  so  polluted  that  in  case  cholera  should  gain 
a  foothold  upon  our  shores  we  have  no  ground  for  hoping  for  the 
favorable  experience  of  the  English  cities  rather  than  the  plague  of 
Hamburg  in  1892. 

THE  faeces  from  a  man  contain  on  an  average  perhaps  1,000,000,- 
ooo  bacteria  per  gram,*  most  of  them  being  the  normal  bacilli  of  the 
intestines,  Bacillus  coli  communis.  Assuming  that  a  man  discharges 
200  grams  or  about  7  ounces  of  faeces  daily,  this  would  give 
200,000,000,000  bacteria  discharged  daily  per  person.  The  number 
of  bacteria  actually  found  in  American  sewage  is  usually  higher, 
often  double  this  number  per  person ;  but  there  are  other  sources 
of  bacteria  in  sewage,  and  in  addition  growths  or  the  reverse  may 
take  place  in  the  sewers,  according  to  circumstances. 

This  number  of  bacteria  in  sewage  is  so  enormously  large  that 
the  addition  of  the  sewage  from  a  village  or  city  to  even  a  large  river 
is  capable  of  affecting  its  entire  bacterial  composition.  Thus  taking 
the  population  of  Lowell  in  1892  at  85,000,  and  the  average  daily 
flow  of  the  Merrimac  at  6000  cubic  feet  per  second,  and  assuming 
that  200,000,000,000  bacteria  are  discharged  daily  in  the  sewage  from 
each  person,  they  would  increase  the  number  in  the  river  by  1160 

*  This  number  was  the  result  of  numerous  counts  made  from  faeces  from  persons 
suffering  with  typhoid  fever  in  the  Lawrence  City  Hospital  in  1891  and  1892.  Mr.  G. 
W.  Fuller  afterward  made  at  the  Lawrence  Experiment  Station  some  further  investi- 
gation of  faeces  from  healthy  people  in  which  the  numbers  were  considerably  lower, 
usually  less  than  200,000,000,  per  gram  and  sometimes  as  low  as  10,000,000  per 
gram. 


2l6  FILTRATION  Of  PUBLIC    WATER-SUPPLIES. 

per  cubic  centimeter,  or  about  300,000  in  an  ordinary  glass  of  water. 
The  average  number  found  in  the  water  eight  miles  below,  at  the 
intake  of  the  Lawrence  water-works,  was  more  than  six  times  as 
great  as  this,  due  in  part  to  the  sewage  of  other  cities  higher  up. 

There  is  every  reason  to  believe  that  the  bulk  of  these  bacteria 
were  harmless  to  the  people  of  Lawrence,  who  drank  them;  but  some 
of  them  were  not.  Faeces  of  people  suffering  from  typhoid  fever 
contain  the  germs  of  .that  disease.  What  proportion  of  the  total 
number  of  bacteria  in  such  faeces  are  injurious  is  not  known;  but  as- 
suming that  one  fourth  only  of  the  total  number  are  typhoid 
germs,  and  supposing  the  faeces  of  one  man  to  be  evenly  mixed 
with  the  whole  daily  average  flow  of  the  river,  it  would  put  one 
typhoid  germ  into  every  glass  of  water  at  the  Lawrence  intake,  and 
at  low  water  several  times  as  many  proportionately  would  be  added. 
This  gives  some  conception  of  the  dilution  required  to  make  a 
polluted  water  safe. 

One  often  hears  of  the  growth  of  disease-germs  in  water,  but  as 
far  as  the  northern  United  States  and  Europe  are  concerned  there  is 
no  evidence  whatever  that  this  ever  takes  place.  There  are  harm- 
less forms  of  bacteria  which  are  capable  of  growing  upon  less  food 
than  the  disease-germs  require  and  they  often  multiply  in  badly- 
polluted  waters.  Typhoid-fever  germs  live  for  a  longer  or  shorter 
period,  and  finally  die  without  growth.  The  few  laboratory  exper- 
iments which  have  seemed  to  show  an  increase  of  typhoid  germs  in 
water  have  been  made  under  conditions  so  widely  different  from 
those  of  natural  watercourses  that  they  have  no  value.* 

*  These  experiments,  so  far  as  they  have  come  to  the  notice  of  the  author,  have 
been  made  with  water  sterilized  by  heating,  usually  in  small  tubes  stoppered  with 
cotton-wool  or  other  organic  matter.  In  this  case  the  water,  no  matter  how  carefully 
purified  in  the  first  place,  becomes  an  infusion  of  organic  matters  capable  of  sup- 
porting bacterial  growths,  and  not  at  all  to  be  compared  to  natural  waters. 

In  experiments  often  repeated  under  my  direction,  carefully  distilled  water  in 
bottles,  most  scrupulously  clean,  with  glass  stoppers,  and  protected  from  dust,  but  not 
sterilized,  has  uniformly  refused  to  support  bacterial  growths  even  when  cautiously 
seeded  at  the  start,  and  the  same  is  usually  true  of  pure  natural  waters.  Some  further 
experiments  showed  hardly  any  bacterial  growth  even  of  the  most  hardy  water  bac- 
teria in  a  solution  i  part  of  peptone  in  i, coo, 000,000  parts  of  distilled  water,  and 
solutions  ten  times  as  strong  only  gave  moderate  growths. 


WATER-SUPPLY  AND   DISEASE— CONCLUSIONS. 

The  proportionate  number  of  cases  of  typhoid  fever  among  the 
users  of  a  polluted  water  varies  with  the  number  of  typhoid  germs 
in  the  water.  Excessive  pollution  causes  severe  epidemics  or  con- 
tinued high  death-rates  according  as  the  infection  is  continued  or 
intermittent.  Slight  infection  causes  relatively  few  cases  of  fever. 
Pittsburg  and  Allegheny,  taking  their  water-supplies  from  below  the 
outlets  of  some  of  their  own  sewers,  have  suffered  severely  (103.2 
and  127.4  deaths  from  typhoid  fever  annually  per  100,000,  respec- 
tively, from  1888  to  1892).  Wheeling,  W.  Va.,  with  similar  condi- 
tions in  1890,  was  even  worse,  a  death  rate  of  345  per  100,000  from 
this  cause  being  reported,  while  Albany  had  only  comparatively 
mild  epidemics  from  the  less  directly  and  grossly  polluted  Hudson. 
Lawrence  and  Lowell,  taking  their  water  from  the  Merrimac,  both 
had  for  many  years  continued  excessive  rates,  increasing  gradually 
with  increasing  pollution  ;  and  the  city  having  the  most  polluted 
source  had  the  higher  rate. 

In  Berlin  and  Altona,  in  winter,  with  open  filters,  epidemics  of 
typhoid  fever  followed  decreased  efficiency  of  filtration,  but  the 
epidemics  were  often  so  mild  that  they  would  have  entirely  escaped 
observation  under  present  American  conditions.  Chicago  has  for 
years  suffered  from  typhoid  fever,  and  the  rate  has  fluctuated,  as 
far  as  reliable  information  can  be  obtained,  with  the  fluctuations  in 
the  pollution  of  the  lake  water.  An  unusual  discharge  of  the 
Chicago  River  results  in  a  higher  death-rate.  Abandoning  the 
shore  inlet  near  the  mouth  of  the  Chicago  River  in  1892,  resulted 
in  the  following  year  in  a  reduction  of  60  per  cent  in  the  typhoid 
fever  death-rate.*  This  reduction  shows,  not  that  the  present  in- 
takes are  safe,  but  simply  that  they  are  less  polluted  than  the  old 
ones  to  an  extent  measured  by  the  reduction  in  the  death-rate. 

It  is  not  supposed  that  in  an  epidemic  of  typhoid  fever  caused  by 
polluted  water  every  single  person  contracts  the  disease  directly  by 

*  The  Water-supply  of  Chicago  :  Its  Source  and  Sanitary  Aspects.  By  Arthur  R. 
Reynolds,  M.D.,  Commissioner  of  Health  of  Chicago,  and  Allen  Hazen.  American 
Public  Health  Association,  1893.  Page  146. 


2 1 8  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

drinking  the  water.  On  the  contrary,  typhoid  fever  is  often  com- 
municated in  other  ways.  If  we  have  in  the  first  place  a  thousand 
cases  in  a  city  caused  directly  by  the  water,  they  will  be  followed 
by  a  large  number  of  other  cases  resulting  directly  from  the  pres- 
ence in  the  city  of  the  first  thousand  cases.  The  conditions  favor- 
ing this  spread  may  vary  in  different  wards,  resulting  in  considerable 
local  variations  in  the  death-rates.  Some  persons  also  will  suffer 
who  did  not  drink  any  tap-water.  These  facts,  always  noted  in 
epidemics,  afford  no  ground  for  refusing  to  believe,  in  the  presence 
of  direct  evidence,  that  the  water  was  the  cause  of  the  fever.  These 
additional  cases  are  the  indirect  if  not  the  direct  result  of  the  water. 
The  broad  fact  that  cities  with  polluted  water-supplies  as  a  rule 
have  high  typhoid-fever  death-rates,  and  cities  with  good  water- 
supplies  do  not  (except  in  the  occasional  cases  of  milk  epidemics, 
or  where  they  are  overrun  by  cases  contracted  in  neighboring 
cities  with  bad  water,  as  is  the  case  with  some  of  Chicago's  suburbs), 
is  at  once  the  best  evidence  of  the  damage  from  bad  water  and 
measure  of  its  extent. 

The  conditions  which  remove  or  destroy  the  sewage  bacteria  in 
a  water  tend  to  make  it  safe.  The  most  important  of  them  are : 
(i)  dilution;  (2)  time,  allowing  the  bacteria  to  die  (sunlight  may  aid 
in  this  process,  although  effective  sunshine  cannot  reach  the  lower 
layer  of  turbid  waters  or  through  ice)  ;  (3)  sedimentation,  allowing 
them  to  go  to  the  bottom,  where  they  eventually  die  ;  and  (4)  natu- 
ral or  artificial  filtration.  In  rivers,  distance  is  mainly  useful  in 
affording  time,  and  also,  under  some  conditions,  in  allowing  oppor- 
tunities for  sedimentation.  Thus  a  distance  of  500  miles  requires 
a  week  for  water  travelling  three  miles  an  hour  to  pass,  and  will 
allow  very  important  changes  to  take  place.  The  old  theory  that 
water  purifies  itself  in  running  a  certain  distance  has  no  adequate 
foundation  as  far  as  bacteria  are  concerned.  Some  purification 
takes  place  with  the  time  involved  in  the  passage,  but  its  extent  has 
been  greatly  overestimated. 

The  time  required  for  the  bacteria  to  die  simply  from  natural 


WATER-SUPPLY  AND   DISEASE— CONCLUSIONS.  2 19 

causes  is  considerable  ;  certainly  not  less  than  three  or  four  weeks 
can  be  depended  upon  with  any  confidence.  In  storage  reservoirs 
this  action  is  often  considerable,  and  it  is  for  this  reason  that 
American  water-supplies  from  large  storage  reservoirs  are,  as  a  rule, 
much  more  healthy  than  those  drawn  from  rivers  or  polluted  lakes, 
even  when  the  sources  of  the  former  are  somewhat  polluted.  The 
water-supplies  of  New  York  and  Boston  may  be  cited  as  examples. 
In  many  other  water-works  operations  the  entire  time  from  the 
pollution  to  the  consumption  of  the  water  is  but  a  few  days  or  even 
less,  and  time  does  not  materially  improve  water  in  this  period. 

Sedimentation  removes  bacteria  only  slowly,  as  might  be  ex- 
pected from  their  exceedingly  small  size ;  and  in  addition  their  spe- 
cific gravity  probably  is  but  slightly  greater  than  that  of  water.  The 
Lawrence  reservoir,  holding  from  10  to  14  days'  supply,  effected, 
by  the  combined  effect  of  time  and  sedimentation,  a  reduction  of  90 
per  cent  of  the  bacteria  in  the  raw  water.  In  spite  of  this  the  city 
suffered  severely  and  continuously  from  fever.  It  would  probably 
have  suffered  even  more,  however,  had  it  not  been  for  this  reduc- 
tion. Nothing  is  known  of  the  removal  of  bacteria  by  sedimenta- 
tion from  flowing  rivers,  but,  considering  the  slowness  with  which 
the  process  takes  place  in  standing  water,  it  is  evident  that  we  can- 
not hope  for  very  much  in  streams,  and  especially  rapid  streams, 
where  the  opportunities  for  sedimentation  are  still  less  favorable. 

Filtration  as  practiced  in  Europe  removes  promptly  and  cer- 
tainly a  very  large  proportion  of  the  bacteria — probably,  under  all 
proper  conditions,  over  99  per  cent,  and  is  thus  much  more  effective 
in  purification  than  even  weeks  of  storage  or  long  flows  in  rivers. 
The  places  using  filtered  water  have,  in  general,  extremely  low 
death-rates  from  typhoid  fever.  The  fever  which  has  occurred 
at  a  few  places  drawing  their  raw  water  from  greatly  polluted 
sources  has  resulted  from  improper  conditions  which  can  be 
avoided,  and  affords  no  ground  for  doubt  of  the  efficiency  of  prop- 
erly conducted  filtration. 


220  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

Corresponding  evidence  has  not  yet  been  produced  in  connec- 
tion with  the  mechanical  filters  which  have  been  largely  used  in 
the  United  States;  but  the  bacterial  efficiencies  secured  with 
them,  under  proper  conditions,  and  with  enough  coagulant,  have 
been  such  as  to  warrant  the  belief  that  they  also  will  serve  to 
greatly  diminish  the  danger  from  such  infection,  although  they 
have  not  shown  themselves  equal  in  this  respect  to  sand  filters. 

The  main  point  is  that  disease-germs  shall  not  be  present  in 
our  drinking-water.  If  they  can  be  kept  out  in  the  first  place  at 
reasonable  expense,  that  is  the  thing  to  do.  Innocence  is  better 
than  repentance.  If  they  cannot  be  kept  out,  we  must  take  them 
out  afterwards;  it  does  not  matter  much  how  this  is  done,  so  long 
as  the  work  is  thorough.  Sedimentation  and  storage  may  accom- 
plish much,  but  their  action  is  too  slow  and  often  uncertain. 
Filtration  properly  carried  out  removes  bacteria  promptly  and 
thoroughly  and  at  a  reasonable  expense. 


APPENDICES. 


APPENDIX  I. 

RULES  OF  THE  GERMAN  GOVERNMENT  IN  REGARD  TO  THE 
FILTRATION  OF  SURFACE-WATERS  USED  FOR  PUBLIC 
WATER-SUPPLIES. 

Rules  somewhat  similar  to  those  of  which  a  translation  is 
given  below  were  first  issued  by  the  Imperial  Board  of  Health  in 
1892.  These  rules  were  regarded  as  unnecessarily  rigid,  and  a 
petition  was  presented  to  the  government  signed  by  37  water- 
works engineers  and  directors  requesting  a  revision.*  As  a  result 
a  conference  was  organized  consisting  of  14  members.f  Kohler 
presided,  and  Koch,  Gaffsky,  Werner,  Gunther,  and  Reincke  repre- 
sented the  Imperial  Board  of  Health.  The  bacteriologists  were 
represented  by  Flu'gge,  Wolffhugel,  and  Frankel,  while  Beer, 
Fischer,  Lindley,  Meyer,  and  Piefke  were  the  engineer  members. 

This  conference  prepared  the  17  articles  given  below  in  the  first 
days  of  January,  1894.  A  little  later  the  first  16  articles  were 
issued  to  all  German  local  authorities,  signed  by  Bosse,  minister  of 
the  "Geistlichen,"  and  Haase,  minister  of  the  interior,  and  they  are 
considered  as  binding  upon  all  water-works  using  surface-water. 
The  bacterial  examinations  were  commenced  April  I,  1894,  by  most 
of  the  cities  which  had  not  previously  had  them. 

*  Journal  fur  Gas-  u.  Wasscrversorgung,  1893,  694. 
f  Journal  fur  Gas-  u.  Wasserversorgung,  1894,  185. 

221 


OF    THE 

UNIVERSITY 


222  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

Although  the  articles  do  not  deal  with  rate  of  filtration,  or  the 
precautions  against  snow  and  ice,  they  have  a  very  great  interest 
both  because  they  are  an  official  expression,  and  on  account  of  the 
personal  standing  of  the  men  who  prepared  them. 

§  i.  In  judging  of  the  quality  of  a  filtered  surface-water  the  fol- 
lowing points  should  be  especially  observed : 

a.  The   operation   of    a   filter   is  to  be  regarded  as  satisfactory 
when  the  filtrate  contains  the  smallest  possible  number  of  bacteria, 
not  exceeding  the  number  which  practical  experience  has  shown  to 
be   attainable  with   good  filtration    at  the  works  in   question.     In 
those  cases  where  there  are  no  previous  records  showing  the  possi- 
bilities  of   the   works   and   the   influence    of  the   local   conditions, 
especially  the  character  of  the  raw  water,  and  until  such  informa- 
tion  is  obtained,  it   is  to   be  taken  as  the  rule  that  a  satisfactory 
filtration   will   never  yield   an  effluent   with    more  than  about   100 
bacteria  per  cubic  centimeter. 

b.  The   filtrate   must  be  as  clear  as  possible,  and,  in  regard  to 
color,  taste,  temperature,  and   chemical   composition,  must  be  no 
worse  than  the  raw  water. 

§  2.  .To  allow  a  complete  and  constant  control  of  the  bacterial 
efficiency  of  filtration,  the  filtrate  from  each  single  filter  must  be 
examined  daily.  Any  sudden  increase  in  the  number  of  bacteria 
should  cause  a  suspicion  of  some  unusual  disturbance  in  the  filter, 
and  should  make  the  superintendent  more  attentive  to  the  possible 
causes  of  it. 

§  3.  Filters  must  be  so  constructed  that  samples  of  the  effluent 
from  any  one  of  them  can  be  taken  at  any  desired  time  for  the 
bacteriological  examination  mentioned  in  §  i. 

§  4.  In  order  to  secure  uniformity  of  method,  the  following  is 
recommended  as  the  standard  method  for  bacterial  examination  : 

The  nutrient  medium  consists  of  10  per  cent  meat  extract  gela- 
tine with  peptone,  10  cc.  of  which  is  used  for  each  experiment. 
Two  samples  of  the  water  under  examination  are  to  be  taken,  one 


APPENDIX  I.  22$ 

of  i  cc.  and  one  of  £  cc.  The  gelatine  is  melted  at  a  temperature 
of  30°  to  35°  C.,  and  mixed  with  the  water  as  thoroughly  as  possible 
in  the  test-tube  by  tipping  back  and  forth,  and  is  then  poured 
upon  a  sterile  glass  plate.  The  plates  are  put  under  a  bell-jar 
which  stands  upon  a  piece  of  blotting-paper  saturated  with  water, 
and  in  a  room  in  which  the  temperature  is  about  20°  C. 

The  resulting  colonies  are  counted  after  48  hours,  and  with  the 
aid  of  a  lens. 

If  the  temperature  of  the  room  in  which  the  plates  are  kept  is 
lower  than  the  above,  the  development  of  the  colonies  is  slower, 
and  the  counting  must  be  correspondingly  postponed. 

If  the  number  of  colonies  in  I  cc.  of  the  water  is  greater  than 
about  100,  the  counting  must  be  done  with  the  help  of  the  WolfT- 
htigel's  apparatus. 

§  5.  The  person  entrusted  with  the  carrying-out  of  the  bacterial 
examinations  must  present  a  certificate  that  he  possesses  the  neces- 
sary qualifications,  and  wherever  possible  he  shall  be  a  regular 
employe  of  the  water-works. 

§  6.  When  the  effluent  from  a  filter  does  not  correspond  to  the 
hygienic  requirements  it  must  not  be  used,  unless  the  cause  of  the 
unsatisfactory  work  has  already  been  removed  during  the  period 
covered  by  the  bacterial  examinations. 

In  case  a  filter  for  more  than  a  very  short  time  yields  a  poor 
effluent,  it  is  to  be  put  out  of  service  until  the  cause  of  the  trouble 
is  found  and  corrected. 

It  is,  however,  recognized  from  past  experience  that  sometimes 
unavoidable  conditions  (high  water,  etc.)  make  it  impossible,  from  an 
engineering  standpoint,  to  secure  an  effluent  of  the  quality  stated  in 
§  I.  In  such  cases  it  will  be  necessary  to  get  along  with  a  poorer 
quality  of  water;  but  at  the  same  time,  if  the  conditions  demand  it 
(outbreak  of  an  epidemic,  etc.),  a  suitable  notice  should  be  issued. 

§  7.  Every  single  filter  must  be  so  built  that,  when  an  inferior 
effluent  results,  which  does  not  conform  to  the  requirements,  it  can 
be  disconnected  from  the  pure-water  pipes  and  the  filtrate  allowed 


224  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

to  be  wasted,  as  mentioned  in  §  6.     This  wasting  should  in  general 
take  place,  so  far  as  the  arrangement  of  the  works  will  permit  it : 

(1)  Immediately  after  scraping  a  filter;  and 

(2)  After  replacing  the  sand  to  the  original  depth. 

The  superintendent  must  himself  judge,  from  previous  ex- 
perience with  the  continual  bacterial  examinations,  whether  it  is 
necessary  to  waste  the  water  after  these  operations,  and,  if  so,  how 
long  a  time  will  probably  elapse  before  the  water  reaches  the 
standard  purity. 

§  8.  The  best  sand-filtration  requires  a  liberal  area  of  filter- 
surface,  allowing  plenty  of  reserve,  to  secure,  under  all  local  con- 
ditions, a  moderate  rate  of  filtration  adapted  to  the  character  of  the 
raw  water. 

§  9.  Every  single  filter  shall  be  independently  regulated,  and  the 
rate  of  filtration,  loss  of  head,  and  character  of  the  effluent  shall  be 
known.  Also  each  filter  shall,  by  itself,  be  capable  of  being  com- 
pletely emptied,  and,  after  scraping,  of  having  filtered  water  intro- 
duced from  below  until  the  sand  is  filled  to  the  surface. 

§  10.  The  velocity  of  filtration  in  each  single  filter  shall  be 
capable  of  being  arranged  to  give  the  most  favorable  results,  and 
shall  be  as  regular  as  possible,  quite  free  from  sudden  changes  or 
interruptions.  On  this  account  reservoirs  must  be  provided  large 
enough  to  balance  the  hourly  fluctuation  in  the  consumption  of 
water. 

§  ii.  The  filters  shall  be  so  arranged  that  their  working  shall 
not  be  influenced  by  the  fluctuating  level  of  the  water  in  the  fil- 
tered-water  reservoir  or  pump-well. 

§  12.  The  loss  of  head  shall  not  be  allowed  to  become  so  great 
as  to  cause  a  breaking  through  of  the  upper  layer  on  the  surface  of 
the  filter.  The  limit  to  which  the  loss  of  head  can  be  allowed  to 
go  without  damage  is  to  be  determined  for  each  works  by  bacterial 
examinations. 

§  13.  Filters  shall  be  constructed  throughout  in  such  a  way  as 
to  insure  the  equal  action  of  every  part  of  their  area. 


APPENDIX  /.  225 

§  14.  The  sides  and  bottoms  of  filters  must  be  made  water-tight, 
and  special  pains  must  be  taken  to  avoid  the  danger  of  passages  or 
loose  places  through  which  the  unfiltered  water  on  the  filter  might 
£'id  its  way  to  the  filtered-water  channels.  To  this  end  special 
pains  should  be  taken  to  make  and  keep  the  ventilators  for  the 
nltered-water  channels  absolutely  tight. 

§  15.  The  thickness  of  the  sand-layer  shall  be  so  great  that 
under  no  circumstances  shall  it  be  reduced  by  scraping  to  less  than 
30  cm.  (—12  inches),  and  it  is  desirable,  so  far  as  local  conditions 
allow,  to  increase  this  minimum  limit. 

Special  attention  must  be  given  to  the  upper  layer  of  sand,  which 
must  be  arranged  and  continually  kept  in  the  condition  most  favor- 
able for  filtration.  For  this  reason  it  is  desirable  that,  after  a  filter 
has  been  reduced  in  thickness  by  scraping  and  is  about  to  be 
refilled,  the  sand  below  the  surface,  as  far  as  it  is  discolored,  should 
be  removed  before  bringing  on  the  new  sand. 

§  1 6.  Every  city  in  the  German  empire  using  sand-filtered  water 
is  requested  to  make  a  quarterly  report  of  its  working  results, 
especially  of  the  bacterial  character  of  the  water  before  and  after 
filtration,  to  the  Imperial  Board  of  Health  (Kaiserlichen  Gesund- 
heitsamt),  which  will  keep  itself  in  communication  with  the  com- 
mission  chosen  by  the  water-works  engineers  in  regard  to  these 
questions ;  and  it  is  believed  that  after  such  statistical  information  is 
obtained  for  a  period  of  about  two  years  some  farther  judgments 
can  be  reached. 

§  17.  The  question  as  to  the  establishment  of  a  permanent 
inspection  of  public  water-works,  and,  if  so,  under  what  conditions, 
can  be  best  answered  after  the  receipt  of  the  information  indicated 
in  §  id 


226  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


APPENDIX  II. 

EXTRACTS   FROM    "  BERICHT    DES    MEDICINAL-INSPECTORATS 
DES   HAMBURGISCHEN   STAATES   FUR   DAS  JAHR  1892." 

THE  following  are  translations  from  Dr.  Reincke's  most  valuable 
report  upon  the  vital  statistics  of  Hamburg  for  1892.  I  much 
regret  that  I  am  unable  to  reproduce  in  full  the  very  complete  and 
instructive  tables  and  diagrams  which  accompany  the  report. 

Diarrhoea  and  Cholera  Infantum  (page  10).  "  It  is  usually 
assumed  that  the  increase  of  diarrhceal  diseases  in  summer  is  to  be 
explained  by  the  high  temperature,  especially  by  the  action  of  the 
heat  upon  the  principal  food  of  infants — milk.  Our  observations, 
however,  indicate  that  a  deeper  cause  must  be  sought."  (Tables 
and  diagrams  of  deaths  from  cholera  infantum  by  months  for 
Hamburg  and  for  Altona  with  the  mean  temperatures,  1871-1892.) 

"  From  these  it  appears  that  the  highest  monthly  mortality  of 
each  year  in  Hamburg  occurred  7  times  in  July,  13  times  in 
August,  and  3  times  in  September,  and  substantially  the  same  in 
Altona.  If  one  compares  the  corresponding  temperatures,  it  is 
found  that  in  the  three  years  1886,  1891,  and  1892,  with  high 
September  mortalities,  especially  the  first  two  of  them,  had  their 
maximum  temperature  much  earlier,  in  fact  earlier  than  usual. 
Throughout,  the  correspondence  between  deaths  and  temperatures 
is  not  well  marked.  Repeated  high  temperatures  in  May  and 
June  have  never  been  followed  by  a  notable  amount  of  cholera 
infantum,  although  such  periods  have  lasted  for  a  considerable 
time.  For  example,  toward  the  end  of  May,  1892,  for  a  long  time 
the  temperature  was  higher  than  in  the  following  August,  when 
the  cholera  infantum  appeared. 


APPENDIX  II.  227 

"  The  following  observations  are  still  more  interesting.  As  is 
seen  from  the  diagram,  in  addition  to  the  annual  rise  in  summer 
there  is  also  a  smaller  increase  in  the  winter,  which  is  especially 
marked  in  Altona.  In  1892  this  winter  outbreak  was  greater  than 
the  summer  one,  and  nearly  as  great  in  1880  and  in  1888.  The 
few  years  when  this  winter  increase  was  not  marked,  1876-7,  1877-8, 
1 88 1-2,  1883-4,  were  warm  winters  in  which  the  mean  temperature 
did  not  go  below  the  freezing-point.  It  is  also  to  be  noted  that 
the  time  of  this  winter  outbreak  is  much  more  variable  than  that 
of  the  summer  one.  In  1887  the  greatest  mortality  was  in  Novem- 
ber;  in  1889  in  February;  in  other  years  in  December  or  January^ 
and  in  Altona,  in  1886  and  1888,  in  March,  which  is  sufficient 
evidence  that  it  was  not  the  result  of  Christmas  festivities. 

"  Farther,  the  winter  diarrhoea  of  Hamburg  and  of  Altona  are 
not  parallel  as  is  the  case  in  summer.  In  Hamburg  the  greatest 
mortality  generally  comes  before  New  Year's ;  in  Altona  one  to  two 
months  later. 

"  In  Bockendahl's  Generalbericht  u'ber  das  offentliche  Gesundheits- 
wesen  der  Provinz  Schleswig-Holstein  fur  das  Jahr  1870,  page  10, 
we  read  :  '  Yet  more  remarkable  was  an  epidemic  of  cholera  infantum 
in  Altona  in  February  which  proved  fatal  to  43  children.  These 
cases  were  distributed  in  every  part  of  the  city,  and  could  not  be 
explained  by  the  health  officer  until  he  ascertained  that  the  water 
company  had  supplied  unfiltered  water  to  the  city.  This  occurred 
for  a  few  days  only  in  January,  and  was  the  only  time  in  the  whole 
year  that  unfiltered  Elbe  water  was  delivered.  However  little 
reason  there  may  be  to  believe  that  there  was  a  connection  between 
these  circumstances,  future  interruptions  of  the  service  of  filtered 
water  should  be  most  critically  watched,  as  only  in  this  way  can 
reliable  conclusions  be  reached.  Without  attempting  to  draw  any 
scientific  conclusions  from  the  fact,  I  cannot  do  less  than  record 
that,  prior  to  the  outbreak  of  cholera  on  August  20,  1871,  unfiltered 
together  with  filtered  water  had  been  supplied  to  the  city  August 
II  to  1 8.  The  action  of  the  authorities  was  then  justified  when 


228  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

they  forbade  in  future  the  supply  of  unfiltered  water  except  in 
cases  of  most  urgent  necessity,  as  in  case  of  general  conflagration," 
and  in  such  a  case,  or  in  case  of  interruption  due  to  broken  pipes, 
that  the  public  should  be  suitably  warned/ 

"  The  author  of  this  paragraph,  Dr.  Kraus,  became  later  the 
health  officer  of  Hamburg,  and  in  an  opinion  written  by  him  in 
1874,  and  now  before  me,  he  most  earnestly  urged  the  adoption  of 
sand-filtration  in  Hamburg,  and  cites  the  above  observations  in 
support  of  his  position.  In  the  annual  report  of  vital  statistics  of 
Hamburg  for  1875  he  says  that  it  is  quite  possible  that  the  addition 
of  unfiltered  Elbe  water  to  milk  is  the  cause  of  the  high  mortality 
from  cholera  infantum,  as  compared  with  London,  and  this  idea 
was  often  afterward  expressed  by  him.  Since  then  so  much  evi- 
dence has  accumulated  that  his  view  may  fairly  be  considered 
proved. 

"  For  the  information  of  readers  not  familiar  with  local  condi- 
tions, a  mention  of  the  sources  of  the  water-supplies  up  to  the  pres- 
ent time  used  by  Hamburg  and  Altona  will  be  useful.  Both  cities 
take  their  entire  water-supplies  from  the  Elbe — Altona  from  a 
point  about  7  miles  below  the  discharge  of  the  sewage  of  both 
cities,  Hamburg  from  about  7  miles  above.  The  raw  water  at 
Altona  is  thus  polluted  by  the  sewage  from  the  population  of  both 
cities,  having  now  together  over  700,000  inhabitants,  and  contains  in 
general  20,000  to  40,000  or  more  bacteria  per  cubic  centimeter. 
The  raw  water  of  Hamburg  has,  however,  according  to  the  time  of 
year  and  tide,  from  200  to  5000,  but  here  also  occasionally  much 
higher  numbers  are  obtained  when  the  ebb  tide  carries  sewage  up 
to  the  intake.  How  often  this  takes  place  is  not  accurately  known, 
but  most  frequently  in  summer  when  the  river  is  low,  more  rarely 
in  winter  and  in  times  of  flood.  Recent  bacterial  examinations 
show  that  it  occurs  much  more  frequently  than  was  formerly  as- 
sumed from  float  experiments.  This  water  is  pumped  directly  to 
the  city  raw,  while  that  for  Altona  is  carefully  filtered. 

"  Years  ago  I  expressed  the  opinion  that  the  repeated  typhoid 


APPENDIX  II.  229 

epidemics  in  Altona  stood  in  direct  connection  with  disturbances  of 
the  action  of  the  filters  by  frost,  which  result  in  the  supply  of 
insufficiently  purified  water.  Wallichs  in  Altona  has  also  come  to 
this  conclusion  as  a  result  of  extended  observation,  and  recently 
Robert  Koch  has  explained  the  little  winter  epidemic  of  cholera  in 
Altona  in  the  same  way,  thus  supporting  our  theory.  When  open, 
filters  are  cleaned  in  cold,  frosty  weather  the  bacteria  in  the  water 
are  not  sufficiently  held  back  by  the  filters.  Such  disturbances  of 
filtration  not  only  preceded  the  explosive  epidemics  of  typhoid 
fever  of  1886,  1887,  1888,  1891,  and  1892,  and  the  cholera  outbreaks 
of  1871  and  1893,  but  also  the  winter  outbreaks  of  cholera  infantum 
which  have  been  so  often  repeated.  It  cannot  be  doubted  that 
these  phenomena  bear  the  relation  to  each  other  of  cause  and 
effect.  It  is  thus  explained  why  in  the  warm  winters  no  such  out- 
breaks have  taken  place,  and  also  why  the  cholera  infantum  in 
winter  is  not  parallel  in  Hamburg  and  Altona. 

"  A  farther  support  of  this  idea  is  furnished  by  Berlin,  where  in 
the  same  way  frost  has  repeatedly  interfered  with  filtration.  In 
the  following  table  are  shown  the  deaths  from  diarrhoea  and  cholera 
infantum  for  a  few  winter  periods  having  unusual  increases  in  mor- 
tality in  comparison  with  the  bacteria  in  the  water-supply."  (These 
tables  show  that  in  March,  1886,  March,  1888,  February — March, 
1889,  and  February,  1891,  high  numbers  of  bacteria  resulted  from 
frost  disturbance  at  the  Stralau  works,  and  in  every  case  they  were 
followed  by  greatly  increased  death-rates  from  diarrhceal  diseases. 
-A.  H.) 

"  No  one  who  sees  this  exhibition  can  doubt  that  here  also  the 
supply  of  inadequately  purified  water  has  every  time  cost  the  lives 
of  many  children."  (100  to  400  or  more  each  time. — A.  H.)  "  Even 
more  conclusive  is  the  evidence,  published  by  the  Berlin  Health 
Office,  that  this  increase  was  confined  to  those  parts  of  the  city  sup- 
plied from  Stralau  "  (with  open  filters. — A.  H.),  "  and  that  the  parts 
supplied  from  the  better  Tegel  works  took  no  part  in  the  outbreaks. 


230  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

which  was  exactly  the  case  with  the  well-known  typhoid  epidemic 
of  February  and  March,  1889.  ...  It  was  also  found  that  those 
children  nursed  by  their  mothers  or  by  wet-nurses  did  not  suffer, 
but  only  those  fed  on  the  milk  of  animals  or  other  substitutes,  and 
which  in  any  case  were  mixed  with  more  or  less  water." 

Under  Cholera,  page  28,  he  says :  "  The  revised  statistics  here 
given  differ  slightly  from  preliminary  figures  previously  issued  and 
widely  published."  (The  full  tables,  which  cannot  be  here  repro- 
duced, show  16,956  cases  and  8605  deaths.  8146  of  the  deaths 
occurred  in  the  month  ending  September  21.  Of  these,  1799 
were  under  5  years  old  ;  776  were  5  to  15;  744,  15  to  25;  3520,  25  to 
50 ;  1369,  50  to  70  ;  and  397  over  70  or  of  unknown  age.  The  bulk 
of  the  cases  were  thus  among  mature  people,  children,  except  very 
young  children,  suffering  the  least  severely  of  any  age  class.) 

"  The  epidemic  began  on  August  16,  in  the  port  where  earlier 
outbreaks  have  also  had  their  origin.  The  original  source  of  the 
infection  has  not  been  ascertained  with  certainty,  but  was  probably 
from  one  of  two  sources.  Either  it  came  from  certain  Jews,  just 
arrived  from  cholera-stricken  Russia,  who  were  encamped  in  large 
numbers  near  the  American  pier,  or  the  infection  came  from  Havre, 
where  cholera  had  been  present  from  the  middle  of  July.  Perhaps 
the  germs  came  in  ships  in  water-ballast  which  was  discharged  at 
Hamburg,  which  is  so  much  more  probable,  as  the  sewage  of  Havre 
is  discharged  directly  into  the  docks. 

"  It  is  remarkable  that  in  Altona,  compared  to  the  total 
number  of  cases,  very  few  children  had  cholera,  while  in  the  epidemic 
of  1871  the  children  suffered  severely.  This  may  be  explained  by 
supposing  that  the  cholera  of  1892  in  Altona  was  not  introduced 
by  water,  but  by  other  means  of  infection.  .  .  . 

"  It  is  well  known  that  the  drinking-water  (of  Hamburg)  is  sup- 
posed to  have  been  from  the  first  the  carrier  of  the  cholera-germs. 
In  support  of  this  view  the  following  points  are  especially  to  be 
noted : 

"  I.  The  explosive  rapidity  of  attack.     The  often-compared  epi- 


APPENDIX  II.  231 

demic  in  Munich  in  1854,  which  could  not  have  come  from  the 
water  is  characteristically  different  in  that  its  rise  was  much  slower 
and  was  followed  by  a  gradual  decline.  In  Hamburg,  with  six 
times  as  large  a  population,  the  height  of  the  epidemic  was  reached 
August  27,  only  12  days  after  the  first  cases  of  sickness,  while  in 
Munich  25  days  were  required.  In  Hamburg  also  the  bulk  of  the 
cases  were  confined  to  12  days,  from  August  25  to  September  5, 
while  in  Munich  the  time  was  twice  as  long. 

"  2.  The  exact  limit  of  the  epidemic  to  the  political  boundary 
between  Hamburg  and  Altona  and  Wandsbeck,  which  also  agrees 
with  the  boundary  between  the  respective  water-supplies,  while 
other  differences  were  entirely  absent.  Hamburg  had  for  1000  in- 
habitants 26.31  cases  and  13.39  deaths,  but  Altona  only  3.81  cases 
and  2.13  deaths,  and  Wandsbeck  3.06  cases  and  2.09  deaths.  .  . 

"  3.  The  old  experience  of  cholera  in  fresh-water  ports,  and  the 
analogy  of  many  earlier  epidemics.  In  this  connection  the  above- 
mentioned  epidemic  of  1871  in  Altona  has  a  special  interest,  even 
though  some  of  the  conclusions  of  Bockendahl's  in  his  report  of 
1871  are  open  to  objection.  First  there  were  3  deaths  August  3, 
which  were  not  at  once  followed  by  others.  Then  unfiltered  Elbe 
water  was  supplied  August  n  to  18.  On  the  igth  an  outbreak  of 
cholera  extended  to  all  parts  of  the  city,  which  reached  its  height 
August  2$  and  26,  and  afterwards  gradually  decreased.  In  all  105 
persons  died  of  cholera  and  1 86  (179  of  them  children)  of  diarrhoea. 
In  Hamburg,  four  times  as  large,  only  141  persons  died  of  cholera 
at  this  time,  thus  proportionately  a  smaller  number.  The  condi- 
tions were  then  the  reverse  of  those  of  1892,  an  infection  of  the 
Altona  water  and  a  comparative  immunity  in  Hamburg. 

"  It  is  objected  that  the  cholera-germs  were  not  found  in  the 
water  in  1892.  To  my  knowledge  they  were  first  looked  for,  and 
then  with  imperfect  methods,  in  the  second  half  of  September.  In 
the  after-epidemics  at  Altona,  they  were  found  in  the  river-water 
by  R.  Koch  by  the  use  of  better  methods. 

"  It  is  quite  evident  that  the  germs  were  also  distributed  by  other 


232  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

methods  than  by  the  city  water,  especially  by  dock-laborers  who 
became  infected  while  at  their  work  and  thus  set  up  little  secondary 
epidemics  where  they  went  or  lived.  .  .  .  These  laborers  and 
sailors,  especially  on  the  smaller  river-boats,  had  an  enormously 
greater  proportionate  amount  of  cholera  than  others.  .  .  .  These 
laborers  do  not  live  exclusively  near  the  water,  but  to  a  measure  in 
all  parts  of  the  city."  (And  in  Altona  and  Wandsbeck.— A.  H.) 

"  Altona  had  5  deaths  from  cholera  December  25  to  January  4,. 
and  19  January  23  to  February  11,  and  no  more.  As  noted  above, 
this  is  attributed  to  the  water-supply,  and  to  defective  filtration  in 
presence  of  frost.  .  .  . 

"  The  cholera  could  never  have  reached  the  proportion  which  it 
did,  had  the  improvements  in  the  drinking-water  been  earlier  com- 
pleted." 

Further  accounts  of  the  water-supplies  of  Altona  and  of  Ham- 
burg and  of  the  new  filtration  works  at  the  latter  city  are  given  in 
Appendices  VII  and  VIII. 


APPENDIX  III.  233 


APPENDIX  III. 

METHODS   OF   SAND-ANALYSIS. 

(From  the  Annual  Report  of  the  Massachusetts  State  Board  of  Health  for  1892.) 

A  KNOWLEDGE  of  the  sizes  of  the  sand-grains  forms  the  basis  of 
many  of  the  computations.  This  information  is  obtained  by  means 
of  mechanical  analyses.  The  sand  sample  is  separated  into  por- 
tions having  grains  of  definite  sizes,  and  from  the  weight  of  the 
several  portions  the  relative  quantities  of  grains  of  any  size  can  be 
computed. 

Collection  of  Samples. — In  shipping  and  handling,  samples  of 
sand  are  best  kept  in  their  natural  moist  condition,  as  there  is  then 
no  tendency  to  separation  into  portions  of  unequal-sized  grains. 
Under  no  circumstances  should  different  materials  be  mixed  in  the 
same  sample.  If  the  material  under  examination  is  not  homogene- 
ous, samples  of  each  grade  should  be  taken  in  separate  bottles,  with 
proper  notes  in  regard  to  location,  quantity,  etc.  Eight-ounce 
wide-necked  bottles  are  most  convenient  for  sand  samples,  but  with 
gravels  a  larger  quantity  is  often  required.  Duplicate  samples  for 
comparison  after  obtaining  the  results  of  analyses  are  often  useful. 

Separation  into  Portions  having  Grains  of  Definite  Sizes. 
— Three  methods  are  employed  for  particles  of  different  sizes — 
hand-picking  for  the  stones,  sieves  for  the  sands,  and  water  elutria- 
tion  for  the  extremely  fine  particles.  Ignition,  or  determination  of 
albuminoid  ammonia,  might  be  added  for  determining  the  quantity 
of  organic  matter,  which,  as  a  matter  of  convenience,  is  assumed  to 
consist  of  particles  less  than  o.oi  millimeter  in  diameter. 


234  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

The  method  of  hand-picking  is  ordinarily  applied  only  to  parti- 
cles which  remain  on  a  sieve  two  meshes  to  an  inch.  The  stones  of 
this  size  are  spread  out  so  that  all  are  in  sight,  and  a  definite  num- 
ber of  the  largest  are  selected  and  weighed.  The  diameter  is  calcu- 
lated from  the  average  weight  by  the  method  to  be  described, 
while  the  percentage  is  reckoned  from  the  total  weight  Another 
set  of  the  largest  remaining  stones  is  then  picked  out  and  weighed 
as  before,  and  so  on  until  the  sample  is  exhausted.  With  a  little 
practice  the  eye  enables  one  to  pick  out  the  largest  stones  quite 
accurately. 

With  smaller  particles  this  process  becomes  too  laborious,  on 
account  of  the  large  number  of  particles,  and  sieves  are  therefore 
used  instead.  The  sand  for  sifting  must  be  entirely  free  from  mois 
ture,  and  is  ordinarily  dried  in  an  oven  at  a  temperature  somewhat 
above  the  boiling-point  The  quantity  taken  for  analysis  should 
rarely  exceed  100-200  grams.  The  sieves  are  made  from  carefully- 
selected  brass-wire  gauze,  having,  as  nearly  as  possible,  square  and 
even-sized  meshes  The  frames  are  of  metal,  fitting  into  each  other 
so  that  several  sieves  can  be  used  at  once  without  loss  of  material. 
It  is  a  great  convenience  to  have  a  mechanical  shaker,  which  will 
take  a  series  of  sieves  and  give  them  a  uniform  and  sufficient  shak- 
ing in  a  short  time  ;  but  without  this  good  results  can  be  obtained 
by  hand-shaking.  A  series  which  has  proved  very  satisfactory  has 
sieves  with  approximately  2,  4,  6,  10,  20,  40,  70,  100,  140,  and  200 
meshes  to  an  inch ;  but  the  exact  numbers  are  of  no  consequence, 
as  the  actual  sizes  of  the  particles  are  relied  upon,  and  not  the  num 
ber  of  meshes  to  an  inch. 

It  can  be  easily  shown  by  experiment  that  when  a  mixed  sand 
is  shaken  upon  a  sieve  the  smaller  particles  pass  first,  and  as  the 
shaking  is  continued  larger  and  larger  particles  pass,  until  the  limit 
is  reached  when  almost  nothing  will  pass.  The  last  and  largest  par- 
ticles passing  are  collected  and  measured,  and  they  represent  the 
separation  of  that  sieve.  The  size  of  separation  of  a  sieve  bears  a 
tolerably  definite  relation  to  the  size  of  the  mesh,  but  the  relation 


APPENDIX  III.  235 

is  not  to  be  depended  upon,  owing  to  the  irregularities  in  the 
meshes  and  also  to  the  fact  that  the  finer  sieves  are  woven  on  a  dif- 
ferent pattern  from  the  coarser  ones,  and  the  particles  passing  the 
finer  sieves  are  somewhat  larger  in  proportion  to  the  mesh  than  is 
the  case  with  the  coarser  sieves.  For  these  reasons  the  sizes  of  the 
sand-grains  are  determined  by  actual  measurements,  regardless  of 
the  size  of  the  mesh  of  the  sieve. 

It  has  not  been  found  practicable  to  extend  the  sieve-separations 
to  particles  below  o.io  millimeter  in  diameter  (corresponding  to  a 
sieve  with  about  200  meshes  to  an  inch),  and  for  such  particles 
elutriation  is  used.  The  portion  passing  the  finest  sieve  contains 
the  greater  part  of  the  organic  matter  of  the  sample,  with  the  ex- 
ception of  roots  and  other  large  undecomposed  matters,  and  it  is 
usually  best  to  remove  this  organic  matter  by  ignition  at  the  lowest 
possible  heat  before  proceeding  to  the  water-separations.  The  loss 
in  weight  is  regarded  as  organic  matter,  and  calculated  as  below 
o.oi  millimeter  in  diameter.  In  case  the  mineral  matter  is  decom- 
posed by  the  necessary  heat,  the  ignition  must  be  omitted,  and  an 
approximate  equivalent  can  be  obtained  by  multiplying  the  albu- 
minoid ammonia  of  the  sample  by  50.*  In  this  case  it  is  necessary 
to  deduct  an  equivalent  amount  from  the  other  fine  portions,  as 
otherwise  the  analyses  when  expressed  in  percentages  would  add 
up  to  more  than  one  hundred. 

Five  grams  of  the  ignited  fine  particles  are  put  in  a  beaker  90 
millimeters  high  and  holding  about  230  cubic  centimeters.  The 
beaker  is  then  nearly  filled  with  distilled  water  at  a  temperature  of 
20°  C,  and  thoroughly  mixed  by  blowing  into  it  air  through  a  glass 
tube.  A  larger  quantity  of  sand  than  5  grams  will  not  settle  uni- 
formly in  the  quantity  of  water  given,  but  less  can  be  used  if  de- 
sired. The  rapidity  of  settlement  depends  upon  the  temperature  of 
the  water,  so  that  it  is  quite  important  that  no  material  variation  in 
temperature  should  occur.  The  mixed  sand  and  water  is  allowed 

*  The  method  of  making  this  determination  was  given  in   the   American   Chemical 
Journal,  vol.   12,  p.  427. 


236  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

to  stand  for  fifteen  seconds,  when  most  of  the  supernatant  liquid,, 
carrying  with  it  the  greater  part  of  the  particles  less  than  0.08  milli- 
meter, is  rapidly  decanted  into  a  suitable  vessel,  and  the  remaining 
sand  is  again  mixed  with  an  equal  amount  of  fresh  water,  which  is 
again  poured  off  after  fifteen  seconds,  carrying  with  it  most  of  the 
remaining  fine  particles.  This  process  is  once  more  repeated,  after 
which  the  remaining  sand  is  allowed  to  drain,  and  is  then  dried  and 
weighed,  and  calculated  as  above  0.08  millimeter  in  diameter.  The 
finer  decanted  sand  will  have  sufficiently  settled  in  a  few  minutes, 
and  the  coarser  parts  at  the  bottom  are  washed  back  into  the 
beaker  and  treated  with  water  exactly  as  before,  except  that  one 
minute  interval  is  now  allowed  for  settling.  The  sand  remaining  is 
calculated  as  above  0.04  millimeter,  and  the  portion  below  0.04  is 
estimated  by  difference,  as  its  direct  determination  is  very  tedious, 
and  no  more  accurate  than  the  estimation  by  difference  when  suffi- 
cient care  is  used. 

Determination  of  the  Sizes  of  the  Sand-grains.  —  The  sizes 
of  the  sand-grains  can  be  determined  in  either  of  two  ways  —  from 
the  weight  of  the  particles  or  from  micrometer  measurements. 
For  convenience  the  size  of  each  particle  is  considered  to  be  the 
diameter  of  a  sphere  of  equal  volume.  When  the  weight  and  spe- 
cific gravity  of  a  particle  are  known,  the  diameter  can  be  readily 
calculated.  The  volume  of  a  sphere  is  \nd*,  and  is  also  equal  to 
the  weight  divided  by  the  specific  gravity.  With  the  Lawrence 
materials  the  specific  gravity  is  uniformly  2.65  within  very  narrow 

limits,  and  we  have  -  =  \nd?.     Solving  for  d  we  obtain  the  for- 


mula d  =  .gVw,  where  d  is  the  diameter  of  a  particle  in  millime- 
ters and  w  its  weight  in  milligrams.  As  the  average  weight  of  par- 
ticles, when  not  too  small,  can  be  determined  with  precision,  this 
method  is  very  accurate,  and  altogether  the  most  satisfactory  for 
particles  above  o.io  millimeter;  that  is,  for  all  sieve  separations. 
For  the  finer  particles  the  method  is  inapplicable,  on  account  of 
the  vast  number  of  particles  to  be  counted  in  the  smallest  portion 


APPENDIX  III.  237 

which  can  be  accurately  weighed,  and  in  these  cases  the  sizes  are 
determined  by  micrometer  measurements.  As  the  sand-grains  are 
not  spherical  or  even  regular  in  shape,  considerable  care  is  required 
to  ascertain  the  true  mean  diameter.  The  most  accurate  method  is 
to  measure  the  long  diameter  and  the  middle  diameter  at  right  an- 
gles to  it,  as  seen  by  a  microscope.  The  short  diameter  is  obtained 
by  a  micrometer  screw,  focussing  first  upon  the  glass  upon  which 
the  particle  rests  and  then  upon  the  highest  point  to  be  found.  The 
mean  diameter  is  then  the  cube  root  of  the  product  of  the  three 
observed  diameters.  The  middle  diameter  is  usually  about  equal 
to  the  mean  diameter,  and  can  generally  be  used  for  it,  avoiding  the 
troublesome  measurement  of  the  short  diameters. 

The  sizes  of  the  separations  of  the  sieves  are  always  determined 
from  the  very  last  sand  which  passes  through  in  the  course  of  an 
analysis,  and  the  results  so  obtained  are  quite  accurate.  With  the 
elutriations  average  samples  are  inspected,  and  estimates  made  of 
the  range  in  size  of  particles  in  each  portion.  Some  stray  particles 
both  above  and  below  the  normal  sizes  are  usually  present,  and 
even  with  the  greatest  care  the  result  is  only  an  approximation  to 
the  truth ;  still,  a  series  of  results  made  in  strictly  the  same  way 
should  be  thoroughly  satisfactory,  notwithstanding  possible  moder- 
ate errors  in  the  absolute  sizes. 

Calculation  of  Results. — When  a  material  has  been  separated 
into  portions,  each  of  which  is  accurately  weighed,  and  the  range  in 
the  sizes  of  grains  in  each  portion  determined,  the  weight  of  the 
particles  finer  than  each  size  of  separation  can  be  calculated,  and 
with  enough  properly  selected  separations  the  results  can  be 
plotted  in  the  form  of  a  diagram,  and  measurements  of  the  curve 
taken  for  intermediate  points  with  a  fair  degree  of  accuracy.  This 
curve  of  results  may  be  drawn  upon  a  uniform  scale,  using  the 
actual  figures  of  sizes  and  of  per  cents  by  weight,  or  the  logarithms 
of  the  figures  may  be  used  in  one  or  both  directions.  The  method 
of  plotting  is  not  of  vital  importance,  and  the  method  for  any  set  of 
materials  which  gives  the  most  easily  and  accurately  drawn  curves 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


is  to  be  preferred.  In  the  diagram  published  in  the  Report  of 
the  Mass.  State  Board  of  Health  for  1891,  page  430,  the  logarith- 
mic scale  was  used  in  one  direction,  but  in  many  instances  the 
logarithmic  scale  can  be  used  to  advantage  in  both  directions. 
With  this  method  it  has  been  found  that  the  curve  is  often  almost 
a  straight  line  through  the  lower  and  most  important  section,  and 
very  accurate  results  are  obtained  even  with  a  smaller  number  of 
separations. 

Examples  of  Calculation  of  Results. — Following  are  exam- 
ples of  representative  analyses,  showing  the  method  of  calculation 
used  with  the  different  methods  of  separation  employed  with 
various  materials. 

I.    ANALYSIS   OF  A   GRAVEL  BY   HAND-PICKING,  11,870  GRAMS 
TAKEN   FOR   ANALYSIS. 


Number  of  Stones 
in  Portion. 
(Largest  Selected 
Stones.) 

Total 
Weight  of 
Portion. 
Grams. 

Average 
Weight  of 
Stones. 
Milligrams. 

Estimated 
Weight  of 
Smallest 
Stones. 
Milligrams. 

Corre- 
sponding 
Size. 
Milli- 
meters. 

Total 
Weight  of 
Stones 
Smaller  than 
this  Size. 

Per  Cent  of 
Total 
Weight 
Smaller  than 
this  Size. 

11,870 

100 

10  

3,  320 

332.OOO 

250  ooo 

56 

8  ceo 

72 

10  

I,Q3O 

IQ3.OOO 

165,000 

49 

6  620 

56 

10  

1,380 

138,000 

I24,OOO 

45 

c,  240 

44 

20  

2,2OO 

1,10,000 

Q3.OOO 

41 

3,O4O 

26 

20                      

I   S2O 

76000 

64  ooo 

36 

I   f^2O 

13 

2O  

I,OOO 

5O,OOO 

36  ooo 

30 

C2O 

4.4- 

2O  

4.6O 

23,000 

10,000 

20 

60 

.5 

10  

AO 

4,OOO 

2,000 

11 

2O 

,2 

Dust  

2O 

The  weight  of  the  smallest  stones  in  a  portion  given  in  the 
fourth  column  is  estimated  in  general  as  about  half-way  between 
the  average  weight  of  all  the  stones  in  that  portion  and  the  average- 
weight  of  the  stones  in  the  next  finer  portion. 

The  final  results  are  shown  by  the  figures  in  full-faced  type  in 
the  last  and  third  from  the  last  columns.  By  plotting  these  figures. 
we  find  that  10  per  cent  of  the  stones  are  less  than  35  millimeters- 
in  diameter,  and  60  per  cent  are  less  than  51  millimeters.  The 
"  uniformity  coefficient,"  as  described  below,  is  the  ratios  of  these 
numbers,  or  1.46,  while  the  "  effective  size  "  is  35  millimeters. 


APPENDIX  III. 


239 


II.  ANALYSIS  OF  A  SAND  BY  MEANS  OF  SIEVES. 
A  portion  of  the  sample  was  dried  in  a  porcelain  dish  in  an  air- 
bath.  Weight  dry,  110.9  grams.  It  was  put  into  a  series  of  sieves 
in  a  mechanical  shaker,  and  given  one  hundred  turns  (equal  to 
about  seven  hundred  single  shakes).  The  sieves  were  then  taken 
apart,  and  the  portion  passing  the  finest  sieve  weighed.  After 
noting  the  weight,  the  sand  remaining  on  the  finest  sieve,  but  pass- 
ing all  the  coarser  sieves,  was  added  to  the  first  and  again  weighed, 
this  process  being  repeated  until  all  the  sample  was  upon  the 
scale,  weighing  110.7  grams,  showing  a  loss  by  handling  of  only  0.2 
gram.  The  figures  were  as  follows : 


Size  of 

Size  of 

Sieve 

Separation 
of  this 

Quantity 
of  Sand 

Per  Cent 
of 

Sieve 

Separation 
of  this 

Quantity 
of  Sand 

Per  Cent 
of 

Marked. 

Sieve. 

Passing. 

Total 

Marked. 

Sieve. 

Passing. 

Total 

Milli- 

Grams. 

Weight. 

Milli- 

Grams. 

Weight. 

meters. 

meters. 

IQO 

,105 

c 

.5 

40 

.46 

S6  7 

51.2 

IAO.  . 

.135 

•  j 
I  .  -l 

1.2 

2O  

.93 

5<j.  / 
80    I 

80.5 

IOO  

.182 

4-  I 

3.7 

10  

2.04 

104  6 

94.3 

60... 

.320 

21    2 

21.0 

6  

3.90 

I  IO  7 

100.0 

Plotting  the  figures  in  heavy-faced  type,  we  find  from  the  curve 
that  IO  and  60  per  cent  respectively  are  finer  than  .25  and  .62  milli- 
meter, and  we  have  for  effective  size,  as  described  above,  .25,  and 
for  uniformity  coefficient  2.5. 

III.   ANALYSIS  OF  A  FINE  MATERIAL  WITH   ELUTRIATION. 

The  entire  sample,  74  grams,  was  taken  for  analysis.  The  sieves; 
used  were  not  the  same  as  those  in  the  previous  analysis,  and 
instead  of  mixing  the  various  portions  on  the  scale  they  were, 
separately  weighed.  The  siftings  were  as  follows  : 

Remaining  on  sieve  marked    10,  above  2.2    millimeters 1.5  grams 

"                 "          "                 "            20,  "  .98  "             7.0          " 

40,  "  .46  "              22.0 

"                  "          "                  "            70,  "  .24  "              20.2          " 

140,  "  .13  "              9.2 

Passing  sieve  140,   below   .13  ..,,   14,1       «« 


240 


FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 


The  14.1  grams  passing  the  140  sieve  were  thoroughly  mixed, 
and  one  third,  4.7  grams,  taken  for  analysis.  After  ignition  just 
below  a  red  heat  in  a  radiator,  the  weight  was  diminished  by  0.47 
gram.  The  portion  above  .08  millimeter  and  between  .04  and  .08 
millimeter,  separated  as  described  above,  weighed  respectively  1.27 
and  1.71  grams,  and  the  portion  below  .04  millimeter  was  esti- 
mated by  difference  [4.7  —  (0.47  -f-  1.27  -|-  1.71)]  to  be  1.25  grams. 
Multiplying  these  quantities  by  3,  we  obtain  the  corresponding 
quantities  for  the  entire  sample,  and  the  calculation  of  quantities 
finer  than  the  various  sizes  can  be  made  as  follows : 


Size  of  Grain. 

Weight. 
Grams. 

Size  of 
Largest 
Particles. 
Millimeters. 

Weight  ot  all 
the  Finer 
Particles. 
Grams. 

Per  Cent  by 
Weight  of 
all  Finer 
Particles. 

Above  2.  20  millimeters  

I  .  CO 

74.OO 

100 

.98-2  20 

7  OO 

2.20 

72    CO 

98 

.46-  .98 

22   OO 

.98 

/*•  y^ 

6c  co 

89 

.24-  .46 

2O   2O 

.46 

AT.     CO 

60 

.IV-  .24                                 

9.  2O 

.24 

2V  ^O 

32 

oi  .4 

^  81 

.13 

14.    IO 

19 

.04-  .08                       

C     11 

.08 

IO    2Q 

14 

.01-  .04                       

7    7C 

.04 

•  y 
^  16 

7 

Loss  on  ignition  (assumed  to  be 
less  than  .01  millimeter)  

I  .41 

.01 

1  .41 

1.9 

By  plotting  the  heavy-faced  figures  we  find  that  10  and  60  per 
cent  are  respectively  finer  than  .055  and  .46  millimeter;  and  we  have 
effective  size  .055  millimeter  and  uniformity  coefficient  8. 

The  effective  size  and  uniformity  coefficient  calculated  in  this 
way  have  proved  to  be  most  useful  in  various  calculations,  particu- 
larly in  estimating  the  friction  between  the  sands  and  gravels  and 
water.  The  remainder  of  the  article  in  the  Report  of  the  Mass. 
State  Board  of  Health  is  devoted  to  a  discussion  of  these  relations 
which  were  mentioned  in  Chapter  III  of  this  volume. 


APPENDIX  IV. 


241 


APPENDIX    IV. 

FILTER    STATISTICS. 

STATISTICS    OF   OPERATION   OF   SAND    FILTERS. 


0 

Cj 

I 

si 

SI" 

JM. 

"0^5 

a 

P 
C 

£§ 

"£>• 

3  V 

nw  S> 

0) 

C/3  C 

^  k.  C 

Place. 

Year  Ending. 

|Su. 

1 

•fj 

h 

III 

OJu><  c 

o 

£ 

^e 

£-0 

lib^ 

—  «  «  = 

c 

1 

ojB 

HI 

rtj  o 

fil 

H 

s 

< 

< 

< 

£ 

March,  1895 

1,620 

4-44. 

3.08 

I  -4^ 

31  .0 

1896 

1,730 

*T*T 

4-75 

3.08 

*  •  *t  3 

i-55 

48.5 

36 

1897 

1,960 

5-40 

3.08 

i-75 

44.0 

45 

1898 

1,940 

5-30 

3.08 

1.72 

36.5 

53 

Amsterdam,  River  

Dec.,       1894 

1.390 

3.80 

5-43 

0.71 

23 

62 

1896 

1,490 

4.08 

5-43 

0-75 

48 

31 

1897 

1,  600 

4.40 

5-43 

0.81 

30 

53 

Amsterdam,  Dunes  

Dec.,       1894 

2,33° 

6.40 

4.94 

.29 

116 

20 

1896 

2,360 

6.50 

4-75 

•37 

90 

26 

1897 

2,290 

6.25 

4-75 

109 

21 

Ashland,  Wis  

Feb.,       1897 

398 

1.09 

0.50 

'18 

4-83 

83 

Mar.,      1896 

13  ooo 

35.60 

1  O 

"    '      1897 

12,900 

35-40 

25.10 

.40 

1898 

13,200 

36.20 

27.00 

•34 

Bremen  

Mar.,      1895 

1,190 

3-27 

2.51 

50 

24 

1896 

1,220 

3-34 

3-21 

.04 

32-5 

38 

1897 

1,280 

3-50 

3-21 

.09 

25-2 

50 

1898 

1,400 

4.10 

3-21 

.28 

34-0 

41 

Mar.        1895 

2,840 

7   80 

5  •  12 

C.O 

44   '      1896 

2,960 

/    "  iJV' 

8.10 

5-12 

'58 

40.0 

74 

1897 

2,990 

8.20 

5.12 

.60 

37 

81 

1898 

3,060 

8.40 

5-12 

.64 

43 

71 

Brunn  

Dec.,       1896 

1,110 

3-04 

.62 

.87 

8.6 

128 

1897 

1,190 

3-25 

.62 

.00 

9.1 

131 

Brunswick  

Mar.,      1895 

815 

2.23 

.48 

.51 

14.8 

55 

1896 

840 

2.30 

.48 

•56 

13-3 

63 

1897 

820 

2.25 

-48 

-52 

13-7 

60 

1898 

870 

2.38 

.48 

.61 

11.9 

73 

Budapest  

Dec.,       1892 

7,360 

20.  20 

3  oo 

6.70 

254 

29 

242 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


STATISTICS    OF   OPERATION    OF   SAND    FILTERS. 


a 

<*-!     U     ° 

C£S 

Q 

Sj 

c 

|| 

|| 

II6 

sl* 

c 

E 

>J 

CA  a 

c  ];•!. 

Place. 

Year  Ending. 

1  5  u 

_o 

"rt 

o 

1^ 

5   C 

.£  ~  rt 

O/*3  °  c 

O 

£ 

u  c 

£•0 

is  ^^ 

«s«! 

1 

"o  « 

rt  ^  u* 

*o  ^  u 

T3'<   S 

l^oo 

rt  u 

fc5  ° 
>  s  *< 

rt  a;  u 

•c  £  ^ 

«3  0.^1 

H 

^ 

< 

^ 

< 

£ 

CoDcn  hcicrcri                       • 

Dec.        1895 

o    Sfi 

200 

^  .  oo 

.  Z.  £ 

"          1896 

2,490 

6.80 

2.88 

2-35 

52 

48 

1897 

2,580 

7.10 

2.  88 

2.47 

54 

48 

Dordrecht  

Dec.,       1894 

365 

I.OO 

o.  56 

1.79 

Frankfort  on  Oder  

Dec.,       1895 

310 

0.85 

0.37 

2.28 

2.9 

107 

"           1896 

325 

0.89 

0.37 

2.40 

7-4 

44 

1897 

356 

0.98 

0.37 

2.65 

8.8 

41 

Hamburg  

Dec.,       1894 

n,450 

31.40 

34-0 

0.92 

350 

33 

1895 

11,700 

32.10 

34-o 

0.94 

275 

43 

1896 

11,500 

31-70 

34-o 

o.93 

266 

43 

1897 

12,000 

32.70 

34-o 

0.96 

285 

42 

1898 

11,900 

32.60 

43-o 

0.76 

246 

48 

Hudson,  N.  Y  

Dec.,       1892 

697 

1.91 

0.74 

2.58 

1893 

543 

1.49 

0.74 

2.OI 

1895 

535, 

1.46 

o  74 

1.98 

Ilion    N.  Y  

Feb.,       1899 

182 

o.  50 

o.  14 

3e7 

i  .  40 

T  ort 

Konigsberg  

Mar.,      1895 

,060 

2.90 

2.70 

•  3  / 

.07 

38.5 

27 

1896 

,085 

2.97 

2.70 

.10 

35.o 

1897 

,085 

2.97 

2.70 

.10 

41.0 

27 

1898 

,140 

3-12 

2.70 

.16 

44.0 

26 

Lawrence  

Dec.,       1894 

,050 

2.88 

2.50 

.15 

10 

105 

1895 

,097 

3-oo 

2.50 

.20 

27 

41 

1896 

.101 

3.02 

2.50 

.20 

30 

37 

1897 

,114 

3-o6 

2.50 

.22 

27 

Liverpool  

Dec.,       1896 

8,520 

23.40 

10.92 

.14 

158 

54 

*  London,   all   filters  but 

Dec.,       1892 

65,783 

1  80 

I09-75 

.64 

90 

not    including    ground 

1893 

195 

116.00 

.68 

water 

1894 

68,700 

1  88 

117.00 

.60 

1895 

76,900 

210 

123.75 

.70 

1896 

1897 

72,482 
73,340 

198 
201 

123.75 
125.00 

.60 

.61 

London,  Chelsea  

Dec.,       1897 

5,370 

14.70 

8.00 

.85 

E    London 

Dec.        1897 

tR  ooo 

o  T    r\c\ 

Dec.,       1897 

1  O  ,  <J<JU 

8,560 

49  •  oo 

j  1  «  <JU 

2i  .  75 

07 

Lambeth  

Dec.,       1897 

10,370' 

28.40 

12.25 

•30 

New  River        

Dec.        1897 

T  ^    *7CO 

A  1     OO 

16.  50 

6O 

Southwark  &  Vauxhall.  . 

Dec.,       1897 

1  3  »  /  5*-J 

14,800 

<+J  >UU 
40.50 

20.50 

West  Middlesex   

Dec.,       1897 

8  QIO 

T  C.    OO 

.6l 

Lubeck  

Mar.,      1895 

1,520 

4-15 

j  5  .  uu 
1.40 

2-95 

16.2 

94 

1896 

1,  600 

4-38 

1.40 

3-13 

24.4 

66 

1897 

1,650 

4-50 

1.40 

3-22 

27.0 

61 

1898 

1,750 

4.80 

1.40 

3-42 

38.5 

45 

*  Some  of  the  companies  secure  some  ground  water  which  they  mix  with  the  filtered  water,  and 
this  is  included  in  the  quantities  for  the  separate  companies,  but  is  excluded  from  the  totals  for  all 
the  companies  by  years. 


APPENDIX  IV. 
STATISTICS    OF   OPERATION   OF   SAND   FILTERS. 


243 


,,I 

X 

1 

c 

;-  o 

II 

3  o 

fe- 

Place. 

Year  Ending. 

ill. 

I 

O 

£ 

V 

E 

^  C 

If 

C/3  C 

EiL- 

jlj 

iBj 

| 
8 

Area  of 
Acres, 

ll 

fJ 

Magdeburg  

Mar.,   1895 

1880 

5-15 

3-76 

•37 

47-5 

40 

1896 

1950 

5-35 

3-76 

.42 

65.0 

30 

1897 

1880 

5-15 

3-76 

•37 

59-0 

32 

1898 

2070 

5-66 

3-76 

-50 

63.0 

33 

Mt.  Vernon,  N.  Y  

Dec.,   1895 

493 

i-35 

I.  10 

.22 

7-3 

68 

1896 

608 

1.66 

1.  10 

•51 

9.2 

66 

1897 

808 

2.21 

1.  10 

.00 

16.6 

49 

1898 

933 

2.56 

1.  10 

•34 

18.4 

51 

Posen  

Mar.,   1895 

305 

0.84 

0.70 

.20 

10.3 

30 

1896 

346 

0.94 

0.70 

•35 

10.4 

33 

. 

1897 

325 

0.89 

0.70 

.27 

10.  I 

32 

1898 

360 

0.99 

0.70 

.42 

9.6 

38 

Poughkeepsie  

Dec.,   1892 

696 

.91 

0.68 

2.81 

14.0 

50 

1893 

667 

.83 

0.68 

2.70 

12.0 

56 

1894 

633 

-73 

0.68 

2-55 

14 

45 

1895 

686 

.88 

0.68 

2.77 

14 

49 

1896 

664 

.82 

0.68 

2.68 

9 

73 

1897 

615 

.69 

1.36 

•24 

1898 

611 

.67 

1.36 

•23 

10.88 

57 

June,   1897 

«;6o 

i  .  1  1 

9  •  3 

60 

"  '   1898 

j^v 

625 

•71 

i.  ii 

•55 

9.0 

70 

Rotterdam*  ***.....  

Dec.   1893 

T  O   *2O 

f\  1O 

T  T 

Stettin  

Mar.,   1895 

1130 

3  10 

2.26 

•37 

26.5 

43 

1896 

1030 

2^83 

2.26 

•25 

15-5 

66 

1897 

980 

2.70 

2.26 

.19 

16.1 

61 

1898 

1020 

2.80 

2.26 

.24 

20.3 

50 

Stockholm  

Dec.,   1895 

2375 

6.50 

2.78 

2-33 

70.0 

34 

1896 

25OO 

6.85 

2.78 

2-45 

68.0 

37 

1897 

2750 

7-50 

3.60 

2.08 

76.0 

36 

Stralsund  

Mar.,   1897 

215 

0.59 

i.  ii 

0-53 

16.0 

13 

1898 

210 

0.58 

i  .  ii 

0.51 

17-3 

12 

Mar.   1805 

IO4O 

2.85 

i  46 

i  06 

13  >  7 

fmf. 

"  "   1896 

1220 

3-34 

1.66 

i  .  y<_» 

2.04 

17.7 

69 

1897 

I27O 

3.48 

2.32 

1.50 

18.7 

68 

1898 

I32O 

3.60 

2.32 

i-54 

2O.  2 

65 

Dec.,   1896 

C  TO 

i  .  40 

o.  60 

2  33 

1  T 

16 

Dec.,   1891 

2OIO 

5  •  5O 

o.  84 

•  •  jj 

6.  50 

g 

"  '   1892 

2150 

5-90 

0.84 

7.00 

10 

215 

1893 

23IO 

6.38 

.19 

5-35 

13 

177 

1894 

2250 

6.15 

.19 

5-i8 

17 

133 

1895 

2460 

6.70 

.19 

5.62 

27 

91 

1896 

2360 

6-45 

.66 

3-88 

30 

79 

1897 

2500 

6.84 

.66 

4-13 

35 

71 

1898 

2730 

7-50 

.66 

4-50 

47 

58 

244  FILTRATION  OF  PUBLIC    WATER-SUPPLIES, 

PARTIAL    LIST   OF   CITIES    USING    SAND    FILTERS. 


Place. 

When 
Built. 

Population. 
1890. 

Area 
of  Filters. 

Number 
of  Filters. 

Average 
Daily  Con- 
sumption. 

UNITED 

1872 
1874 
i87(?) 
1893 
i893 
1893 
1894 
1894 
1895 
1895 
1895 
1896 
1896 
1897 
1897 
1898 
1898 
1899 
1899 
1899 

STATES. 

24,000 
9,970 

3,857 
3,268 

44,654 
4,057 
10,830 

4,979 
9,956 
9,956 
1-744 
4,142 
2,288 
500 
6,207 
8,783 
826 
1,200 
94.923 
13,634 

1.36 
0.74 
0.14 
O.  II 
2.50 
0.14 
I.  10 

0.42 
0.25 
0.50 

O.  12 
0.28 
0.92 
0.03 
0.50 
0.76 
0-52 
O.  12 
5-60 
I.  2O 

3 
2 

3 

I 
I 
2 

3 

I 
I 

3 
i 

2 
2 
2 
I 

I 

3 

2 

8 
3 

1.67 
1-50 
0.70 
0.09 
3.00 
0.50 
1.66 

Hudson    N    Y     

Ilion    NY                  ... 

Mount  Vernon    N    Y 

Grand  Forks    N.  D  

Milford    Mass                      •  • 

o.  70 
1.09 
0.03 
0.25 
o-93 

O.  IO 

Ashland    Wis  

Hamilton    N.  Y             

Far  Rockaway    NY          

Red  Bank    N    J       .          

Somerswoith    N    H    

Little  Falls    N    Y  

0.15 

I  I  .  OO* 

3-50 

Albany    N    Y          

Rock  Island    Illinois. 

Total 

259,774 
OLUMBIA. 
16,841 
AMERICA. 
500,000 

17.31 
0.82 
4-15 

Filters 

45 

3 

3 
reported 

26.87 
1.  80 

BRITISH  C 

SOUTH   A 

.Montevidio  

HOLLAND. 


290,000 

6.  ^o 

18 

13  .00 

*The  Hague         

191  ooo 

2.88 

6 

4    2O 

2C  aoo 

i  ^ 

c 

o  68 

140  ooo 

o  60 

i  .40 

C7  ooo 

OCQ 

2 

^4  IOO 

o.  56 

2 

i  .00 

OQ  7OO 

O.  *?! 

2 

IO  OOO 

1  8  ooo 

44  2OO 

Middelburp- 

1  7  ooo 

Total  

1,414,021 

22.75 

47 

31.48 

*  Exclusive  of  gravity  supplies. 


APPENDIX  IV. 


245 


PARTIAL   LIST   OF   CITIES    USING   SAND    FILTERS. 
GREAT   BRITAIN. 


Place. 

When 
Built. 

Population. 

Area 
of  Filters. 

Number 
of  Filters. 

Average 
Daily  Con- 
sumption. 

5  030  267 

125  oo 

1  2O 

2OO   OO* 

7QO  OOO 

jo  Q2 

26    6?/ 

74Q  OOO 

S..OO 

IO 

18  oo 

Lee(js          

420  ooo 

6.00 

8 

17    QQ> 

436  260 

4   62 

6 

13    31 

22O  OO5 

2    ^O 

47t 

York                                    

72  08*? 

2    O4 

6 

3OO 

2Q2  364 

2.OO 

I8.OO 

41  OOO 

I    32 

7 

Wakefield  

q6  8m 

I    25 

Carlisle              

40  ooo 

O   QO 

17  821 

o.  25 

42  ooo 

680  140 

IQ    OC. 

130  ooo 

4    jo 

250  ooo 

6  60 

Chester                                        .... 

40  ooo 

Halifax               

217  OOO 

e    T« 

20  ooo 

Middlesboroucrh        .        

l87  HT 

II     1O 

320  ooo 

14  oo 

Ijc  8OO 

51O> 

co  OOO 

I    ^Qi 

I  I  a  864 

4    2O 

71  c.  ?8 

76  41O 

lU" 

34t 

Wigan    

60  ooo 

I    22 

4s,  OOO 

. 

IQ<1 

Total  .  . 

IO.IQQ.7l8 

161.80 

161 

382.73 

GERMANY. 


I  746  424 

31  41? 

ce 

jj-w 
36  oo> 

380  ooo 

512 

8  20 

217  o67 

o  76 

j  j_ 

e  661 

T  C7  CQO 

321 

12 

3C.O 

l62  427 

q  O8 

M 

5  JO- 

176  ooo 

2  7O 

7 

300 

IO2  516 

2  32 

4  oo» 

Stettin  

I4C  OOO 

2  26 

3  .00 

Lubeck     .         ... 

70  ooo 

14O 

5 

100  883 

I  48 

2-JQ 

qo  IO1* 

I  II 

6 

o  60 

4Q  8oi 

I  II 

I  £.4 

46  8«;2 

o  06 

6 

I  4O 

7C.  OOO 

o  70 

36  ooo 

o  65 

o  50 

164  74^ 

O  ^Q 

246 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


PARTIAL   LIST   OF    CITIES    USING    SAND    FILTERS 
GERMANY — Continued. 


Place. 

When 
Built. 

Population. 

Area 
of  Filters. 

Number 
of  Filters. 

Average 
Daily  Con- 
sumption. 

3O,OOO 
20,729 
59.l6l 
69,214 
30,000 
20,154 
6,214 
22,000 

0.50 
0.42 
0-37 
0.31 
0.25 
O.2O 
0.14 
0.13 

3 
3 

5 

4 

0.64 

0.89 
1.50 
0.20 

O.  10 
0.30 

Kiel 

Tilsit 

Gluckstadt             «      •  •  

Wandsbeck     

Total 

4,639,080 
>EAN    FILT1 

106.22 
iRS. 

185 

117.13 

OTHER    EURO! 

ASIA. 


e    Re 

380  ooo 

jy  .uu 

8  oo 

) 

(        1    8e. 

Neuilly  sur  Marne         

\      200,000 

1         211 

T  C 

340  ooo 

2  88 

6  80 

274  OOO 

o    78 

7    OO 

240  ooo 

2    IO 

8 

2    OO 

Zurich      

06  810 

i  66 

7  oo 

i  62 

'i    04 

Total.. 

2.084.810 

•14.74 

88 

88.84 

A  •  v/ 

i-37 

1.22 

0.88 
0.67 

0.58 

821,000 

4 
4 
6 

3 

110,000 
466,000 

Total 

1,397,000 
rtARY. 

6.69 

23 

SUM! 

British  Columbia  

16  841 

O.82 

•3 

i  So 

500  ooo 

4T  C 

Holland 

I  414  O2I 

22    7^ 

47 

31  48 

IO   IQQ   7^8 

161  80 

161 

182    71 

4  639  080 

IO6    22 

iS«; 

117    11 

Other  Kuropean  countries     •  • 

2  Q84  S'lQ 

^4.74 

88 

88  84 

I^Q7  OOO 

6  60 

21 

Total  

21,411,293 

354.48 

555 

648.8=; 

APPENDIX  IV. 


247 


LIST     OF     CITIES     AND     TOWNS     USING      MECHANICAL      FILTERS. 
ARRANGED    BY    POPULATIONS. 

Abbreviations.— P.,  Pressure  filters;  G.,  Gravity  filters;  J.,  Jewell  system;  N.  Y.,  New  York  sys- 
.    in;  W.,  Warren  system;  C.,  Continental  system;  Am.,  American  system. 


Place. 

Population, 
1890. 

Filters  First  Installed. 

Nominal  Capacity  of 
Filters,  1899  ; 
Million  Gallons. 

Average  Consumption, 
Million  Gallons; 
Water  Works  Manual. 

C 

$ 

i 

4J 
£0; 
^ 

8 

< 

Filter  System. 

108  204 

2260 

Special 

Atlanta    Ga  

f)C    C7-1 

1887 

8 

A     KJ. 

2056 

NY       P. 

St    Joseph    Mo                   .  •  • 

C2  12J. 

1898 

IO    2 

o8d.2 

I      G 

Oakland    Cal  

48  682 

1801 

5 

IO 

IQ6o 

N    Y      P 

Kansas  City,  Kan  
Wilkesbarre    Pa  * 

38,316 
07  718 

1898 

6 

TO 

2 

2260 
3166 

J.     G. 
T       G 

Norfolk    Va 

o  i   §71 

1800 

5 

q    c 

2  1  12 

j.     \j. 
T      G 

-IT   aoo 

1800 

5 

T,    8 

21  12 

N    Y      G 

Ouincy    111             

Of)   J.QJ. 

1892 

I    2 

1582 

T      G 

Dubuque    Iowa  "f  .  «  «  

•JO    ^I  I 

1800 

2 

880 

G 

Terre  Haute    Ind  

•3Q    217 

1800 

3    \ 

1076 

N.  Y.     P. 

Elmira    N.  Y  

2Q  708 

1807 

6 

3    1 
•j 

226 
2O^d 

J.     G. 

J      G 

2Q   IOO 

1887 

2O8o 

J  &  N   Y      P 

26  872 

1801 

7    •? 

q 

2^SO 

Am.  P 

Little  Rock    Ark  

oc  S7J. 

1891 

5e 

I  ^dJ. 

Am    J    &JN  Y    P. 

oe  6<12 

1887 

Ie 

•7QO 

N.  Y      P 

Oshkosh    Wis  

22  836 

1801 

2j 

2    i 

c  en 

W      G 

22   7J.6 

180-1 

i  6«; 

IJ.^7 

J     W     &  N   Y. 

22   <^6^ 

i8o.<i 

124.1 

T      G 

Knoxville    Tenn 

10V4 
180  t 

•  3 

I    O1? 

A-^H-J 
I4.OJ. 

j.     \j. 
W      G 

Lexington    Kv 

21    ^67 

jgoe 

2 

*«VJ 

I    2 

678 

T      G 

Kingston,  N.  Y  

21   26l 

l8Q7 

I    c 

1  1  2O 

N.  Y.     P. 

York    Penna  

2O  7QT 

l8oo 

2      '!*] 

1408 

I      G 

2O  5OO 

1896 

2 

780 

W      G. 

Newport    R.  I  

IQ  J.67 

2    I 

Special 

1807 

W      G 

Ay>  juj 
18  020 

1806 

2.  5 

2 

OCX 

J      G- 

Elgin    111   

17  82-; 

1888 

40 

j 

780 

Am      P 

Decatur    111  

16  841 

180-7 

2 

1008 

W      G 

Belleville    111  

i  ^  161 

I 

o  6 

0-JQ 

I      G 

Columbia    S    C 

I  SQ2 

678 

T      G 

Keokuk    la 

1D>  J->J 

180^ 

980 

NY      P 

Ottutnwa    la 

14  ooi 

i8oc 

2 

I    2 

678 

T      G 

Rock  Island,  111.*  
Raleigh    N.  C  

13,634 

12  678 

1887 

2 
I 

3-5 
j 

4-5? 

2QO 

J.     G. 

NY      P. 

Shreveport    La  .... 

A     Q7Q 

1880 

I 

•JI2 

N.  Y.     P. 

II  6oO 

1808 

A 

2 

I4O8 

N.  Y.     G. 

*  Not  in  use. 


t  Under  construction. 


248  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

CITIES   AND    TOWNS    USING   MECHANICAL   FILTERS. 


\ 

Place. 

Population, 
1890. 

Filters  First  Installed. 

Nominal  Capacity  of 
Filters,  1899  ; 
Million  Gallons. 

Average  Consumption, 
Million  Gallons: 
Water  Works  Manual. 

£ 
jf 

e 

!l 

a 

V 

< 

Filter  System. 

Charlotte    N    C    

II  557 

1896 

j 

o  ^ 

5^O 

N    Y      G 

II  4Q4 

1891 

O  4 

O   7 

116 

N.  Y      P 

Streator   111      •       

II  414 

IOO 

Western  &  Am     P 

Hornelsville    N    Yf  

10  966 

1800 

1  •  J 

7OO 

NY      P 

jo  527 

1887 

o  6 

i  5 

IOO 

W 

St    Thomas    Ont  

jO  77o 

1891 

2    ^ 

o  6 

7OO 

NY      P 

Cairo    111            

jO  724 

1889 

o  8 

2e 

IQ7 

NY      P 

Alton    111  

jO  2Q4 

1898 

j 

IO56 

N    Y      G 

Asheville    N    C     

IO  215 

1889 

j 

Oac 

q  j2 

NY      P 

jo  131 

1887 

2 

O  4 

5Q2 

NY      P 

10  108 

1800 

2 

7O4 

N.  Y.     G. 

Beaver  Falls    Pa 

970  e 

N    Y 

9,710 

•  3 

O   7^ 

N    Y. 

Chatham    Ont      

9O52 

tgnc 

OA 

280 

N    Y.     P 

8  756 

1800 

I    75 

OA  C 

565 

T      G 

Athens    Ga            

8  610 

1801 

1 

O4^ 

42O 

W      G. 

East  Providence    R    I.  ... 

8  42^ 

1800 

O    5 

176 

J.     G 

Winston    N    C           

8  018 

J8O5 

O    5 

O    "\ 

156 

W.     G. 

7008 

1896 

226 

T      G 

Clarksville   Tenn.f  

>yy° 

7  024 

•1800 

T    5 

o.  «? 

7Od 

J      G 

Stevens  Point    Wis  

7  806 

1889 

O    % 

O    25 

156 

N.  Y.     P. 

Carlisle    Pa            

7  620 

1896 

T        C 

•JOQ 

J      G 

7  2QO 

i8tn 

I    5 

0.85 

275 

W.     G. 

72^1 

1888 

I  .  "\ 

QO4 

N.  Y.     P. 

7  2OO 

1891 

O    5 

O    "\ 

I  5O 

T. 

St    Hyacinthe    Que  

7  Ql6 

1898 

I 

o  84 

2Q4 

J.     P. 

Rome    Ga  "f  

6  QSI7 

1800 

I    5 

I    o 

528 

J      G. 

Westerly    R    I  

6  813 

1896 

I.  5 

O   "375 

^06 

N.  Y.     G. 

Mernll    Wis 

6  809 

1807 

OOQ 

J      ^ 

6  767 

1800 

I.  25 

I 

528 

J.     G. 

6  7^6 

1804 

2 

0.6 

452 

J.     G. 

6  674 

1891 

j    e 

O   7 

565 

J.     G. 

Somerville,  N.  J  ... 
Athol    Mass        

6,417 

6   ^IQ 

1885 
1888 

1.9 
I    5 

0-75 
O    5 

552 
•35O 

N.  Y.     P. 
N.  Y.     P. 

Owego    N    Y  

6  200 

1887 

1 

O.  75 

274 

N.  Y.     P. 

6  OI2 

1887 

o  6 

O.  77 

IOO 

W. 

Bucyrus    Ohio    

e  074. 

1887 

o.  % 

o.  55 

156 

N.  Y.     P. 

Warren    Ohio 

5070 

1896 

T    e 

1  .  5 

J.62 

W.     G. 

Hopkinsville    Ky          .... 

c  Rv'i 

l8o5 

O.  5 

O    15 

I4O 

N.  Y.     P. 

Brainerd    Minn                  .  . 

57O7 

1807 

O    5 

156 

N.  Y.     P. 

5  616 

1889 

o.  5 

156 

N.  Y.     P. 

Niagara  Falls    N.  Y  

C     CQ2 

I8o6 

4    5 

2.62 

IOIQ 

J.     G. 

*  Not  in  use. 


t  Under  construction. 


APPENDIX  IV. 
CITIES   AND   TOWNS    USING    MECHANICAL   FILTERS. 


249 


Place. 

|| 

s  First  Installed. 

*o 

>»    i« 

y 

3*3 

ill 

ipe  Consumption, 
lion  Gallons: 
Ler  Works  Manual. 

of  Filters,  Sq.  Ft., 
1899. 

Filter  System. 

f 

1 

£ 

|ES 
z 

2X* 

« 

W 

< 

c  485 

iScn 

o.o 

O.  7 

2C2 

W       G 

Winfield,  Kaa  

5184 

1804 

I 

T}6 

W.     G. 

COQO 

1888 

o  8 

242 

NY      P   &  G 

CQ7Q 

1880 

O   4 

128 

NY      P 

486^ 

1806 

1  .  5 

jqc6 

T      G 

Sidney    Ohio  * 

48^0 

Oe 

N    Y 

4780 

1880 

O.  3 

0.4 

66 

NY      P 

4748 

1888 

j 

o  6 

oc  T 

NY      P 

468-} 

1802 

O   OQ 

2O 

NY      P 

jeen 

1800 

O    ^ 

O.  I7£i 

176 

T      G 

\Vinchester   K.y   

4CTQ 

1804 

O.  7C 

O.  IO7 

152 

T      P 

4.11  8 

1889 

Oe 

Ooe 

TC6 

NY      P 

Kufaula.    Ala.                    •• 

J.^O-1 

1807 

Oe 

IJO 

NY      P 

4^0 

1888 

0.8 

o.  175 

156 

N.  Y.     P 

Exeter    N    H 

4284 

1887 

O    1  14 

O  .  I7Q 

•J/l 

NY      P 

42*32 

1800 

O    S 

O    S 

i«;6 

NY      P 

Lake  Forest    III     

42O^ 

1802 

I 

168 

T      P 

Henderson    N    C 

1800 

Ooc 

118 

W      G 

.4.088 

1806 

I 

o.  198 

n6 

W      G 

Goldsboro    N    C 

4OI7 

1896 

Or 

O    I 

i«;6 

W      G 

Rich  Hill    Mo     

4.OO8 

1891 

O.  $ 

O.  24 

140 

N.  Y.     P. 

Mt    Pleasant    la      .  .  .        . 

•JQQ7 

1888 

O    ^ 

i«;6 

NY      P 

388O 

1890 

O    2 

60 

NY      P 

Brandon    Manitoba      

•3773 

1803 

I 

O   ^6 

24O 

NY      P 

Danville    Ky       .  .          .... 

1766 

1804 

O    $ 

O.  I 

1  4O 

N.  Y      P. 

0612 

i8cn 

I 

O.oS 

226 

J      G- 

qei4 

1806 

O.  5 

o.  s 

I56 

N.  Y.     P. 

Ashburv  Park    N   J 

oeoo 

2 

o  «; 

67O 

c 

-J4H 

1895 

O.  <? 

0.06 

156 

W.     G. 

aao8 

1896 

O.5 

0.84 

147 

J.     P. 

Milledgeville   Ga     

•j-322 

igo-i 

O.  S 

156 

N.  Y       P. 

Carlinville    111    

<J2Q/? 

O.  I 

38 

Am.  or  Jackson. 

Oettvsburg    Pa  

0221 

1804 

o  ^ 

0.075 

78 

W.     G. 

•3127 

iSqi 

o.  75 

0.25 

129 

Am.     P. 

OQOO 

igoa 

O    2*> 

34. 

NY       P 

Paola    Kan  

2Q4T 

1887 

0.25 

0.45 

66 

N.  Y.     P. 

Benwood    W    Va  f 

1800 

J 

ao6 

J      G 

Oadsden     Ala       ... 

•*yj4 

2OX)I 

ioyy 

1887 

I  •  ^25 

4^0 

N.  Y.     P.  &  G. 

Lamar    Mo  

2860 

1801 

O.25 

78 

N.  Y.     P. 

27^7 

i8oc 

O   4 

O    1 

IOO 

NY      P. 

272^ 

1888 

O    2 

O    O7  <s 

CQ 

N.  Y.     P. 

Renfrew    Ont  •       •  • 

26l  I 

1807 

O.4^2 

IOO 

N.  Y.     P. 

*  Not  in  use. 


t  Under  construction. 


250 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


CITIES   AND    TOWNS    USING   MECHANICAL   FILTERS. 


Place. 

Population, 
1890. 

Filters  First  Installed. 

Nominal  Capacity  of 
Filters,  1899  ? 
Million  Gallons. 

Average  Consumption, 
Million  Gallons; 
Water  Works  Manual. 

Area  of  Filters,  Sq.  Ft., 
1899. 

Filter  System. 

2C.7A 

i8cn 

O    ^ 

O.3 

IJ.O 

N.  Y.     P. 

Holden,  Mo  

2520 
227Q 

1893 

O.2 

0.05 

IOO 
*7O 

N.  Y.     P. 

T 

Council  Grove,  Kan  
Wakefield    R    I  * 

2211 
2  1  7O 

1898 

0-5 

OT  C 

0.08 
O    2% 

78 

N.Y. 

N    Y 

21  1  5 

1890 

OOC 

78 

NY      P 

Attica    N    Y 

IQQA 

1896 

OA 

IOO 

NY      P. 

Hightstown    N    T                . 

Tg7C 

1800 

OOC 

o  02*; 

78 

N   Y      G 

1803 

1896 

O    ^ 

78 

W.     G, 

1776 

1800 

O    ^ 

1  40 

N.  Y.     P. 

Rogers  Park    111    

1708 

1889 

O     d 

O.  •*<? 

IOO 

N.  Y.     P. 

Eatonton    Ga                 •  •  . 

1682 

1807 

O    ^ 

jq2 

N.  Y.     G. 

•Caldwell    Kan      

1642 

1890 

O    ^ 

1^6 

N.  Y.     P. 

LaGrange    Tex  

1626 

1891 

O    2^ 

04 

N.  Y.     P. 

Richfield  Springs    N    Y 

162^ 

1889 

IOO 

NY      P 

Valatie    N    Y 

7107 

u-  J3 
OT  e 

en 

N    Y 

T2C-3 

O    I 

N.  Y. 

Mechanics  Falls     Me 

IO3O 

1898 

O72 

176 

W.     G. 

New  Bethlehem    Pa     .... 

IO26 

1800 

O    I 

CQ 

J.     G. 

Fairmount    \V    Va 

IO23 

1898 

j 

280 

N.  Y.     P. 

Atlantic  Highlands,  N.  J.. 
Rumford  Falls    Me 

945 

898 

T$n7 

0-3 

Or 

0.109 

130 
us 

C. 
W      G 

109/ 
1880 

Oc 

TCfi 

NY      P 

6^O 

1889 

I 

O.  I 

176 

W.     G. 

Porters  ville    Cal  

606 

1890 

O.  I^I 

0.060 

34 

N.  Y.     P. 

1896 

0.046 

280 

N.  Y.     P. 

Pickering  Creek    Pa 

1896 

O7C 

2-3  A 

W.     G. 

Overbrook    Penna              • 

jgQC 

Ooe 

78 

W.     G. 

Vandergrift    Pa  

180*7 

Oc 

Tc6 

W.     G. 

Frazerville    P   Qf  

ioy/ 
l8oo 

O   2 

78 

N    Y.     G. 

l8OQ 

O    12 

CQ 

N.  Y.     G. 

7800 

612 

T      G 

West  Reading,  Pa  

ioyy 

O.O7 

W.     G. 

Totals  

i  565  881 

2C2 

108 

77  806 

*  Not  in  use. 


t  Under  construction. 


Special  filters,  neither  sand  nor  mechanical  :  Wilmington,  Del.;  Pop.,  61,431; 
area,  10,000  sq.  ft.;  nominal  capacity,  10  million  gallons.  See  Eng.  News, 
Vol.  40,  p.  146. 


APPENDIX  IV,  251 

NOTES   REGARDING   SAND   FILTERS   IN   THE   UNITED   STATES. 

POUGHKEEPSIE,  N.  Y.  Designed  by  James  P.  Kirkwood,  built 
in  1872,  was  the  earliest  of  its  kind  in  the  United  States.  It 
was  enlarged  by  the  Superintendent,  Charles  E.  Fowler,  in  1896. 
The  walls  of  the  original  filters  were  of  rubble,  and  in  course  of  time 
developed  cracks  and  leaked  badly.  The  walls  of  the  new  filter  are 
of  rubble,  faced  with  vitrified  brick.  The  filters  treat  the  water  of 
the  Hudson  River,  which  is  sewage-polluted  and  more  or  less 
muddy.  Description  :  Jour.  N.  E.  Water  Works  Assoc.,  Vol.  12, 
p.  209. 

HUDSON,  N.  Y.  Designed  by  James  P.  Kirkwood,  built  in  1874, 
enlarged  in  1888.  The  filters  are  open  and  are  used  for  treating  the 
Hudson  River  water,  which  is  sewage-polluted  and  more  or  less 
muddy.  Description  :  Eng.  News,  Vol.  31,  p.  487, 

ST.  JOHNSBURY,  VT.  (E.  &  T.  Fairbanks  &  Co.)  These  filters 
were  built  about  30  years  ago,  and  have  been  recently  enlarged. 
The  filters  were  originally  open,  but  were  afterwards  covered  with  a 
roof.  The  single  roof  proved  inadequate  to  keep  them  from  freez- 
ing, and  a  second  roof  was  added  inside  and  under  the  main  roof. 
They  are  used  for  filtering  pond  water,  which  is  quite  clear  and  not 
subject  to  much  pollution.  The  water  supply  is  one  of  two,  the 
other  is  the  town  supply  and  is  taken  from  the  Passumpsic  River. 
No  published  description. 

NANTUCKET,  MASS.  Designed  by  J.  B.  Rider,  built  in  1892. 
This  filter  is  used  to  remove  organisms  from  the  reservoir  water 
supply.  It  is  only  used  when  the  organisms  are  troublesome,  and  is 
satisfactory  in  preventing  the  tastes  and  odors  which  formerly  re- 
sulted from  their  presence.  Description  :  Jour.  N.  E.  Water  Works 
Assoc.,  Vol.  8,  p.  171  ;  Eng.  News,  Vol.  31,  p.  336. 

LAWRENCE,  MASS.  Designed  by  Hiram  F.  Mills,  built  in 
1892-3,  and  put  in  operation  September,  1893.  It  is  used  for  treat- 
ing the  water  of  the  Merrimac  River,  which  contains  a  large  amount 


252  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

of  sewage.  Description :  Report  of  the  Mass.  State  Board  of 
Health,  1893,  p.  543  ;  Jour.  N.  E.  Water  Works  Assoc.,  Vol.  9, 
p.  44 ;  Eng.  News,  Vol.  30,  p.  97. 

ILION,  N.  Y.  Designed  by  the  Stanwix  Engineering  Company 
and  are  used  for  treating  reservoir  water,  which  is  generally  clear 
and  not  subject  to  pollution.  Description  :  Eng.  News,  Vol.  31, 
p.  466. 

MOUNT  VERNON,  N.  Y.  (New  York  Suburban  Water  Company.) 
Designed  by  J.  N.Chester,  built  in  1894.  These  filters  are  similar  in 
general  construction  to  the  Lawrence  filter,  although  the  dimensions 
both  vertical  and  horizontal  are  reduced,  and  the  area  is  divided  into 
three  parts.  The  filters  are  used  for  treating  reservoir  water,  which 
is  generally  quite  clear,  but  which  is  polluted  by  a  considerable 
amount  of  sewage.  Since  the  use  of  filters  the  reduction  in  the 
typhoid  fever  death-rate  has  been  very  great.  Description  :  Eng. 
News,  Vol.  32,  p.  155. 

MlLFORD,  MASS.  Designed  by  F.  L.  Northrop.  This  filter  is 
very  simple  in  construction,  and  is  used  for  filtering  Charles  River 
water  as  an  auxiliary  supply.  Description  :  Jour.  N.  E.  Water 
Works  Assoc.,  Vol.  10,  p.  262. 

GRAND  FORKS,  N.  D.  Designed  by  W.  S.  Russell.  These  filters 
are  covered  with  roofs.  They  treat  the  water  from  the  Red  River, 
which  is  very  muddy,  and  also  sewage-polluted,  and  which  formerly 
caused  typhoid  fever.  Description  :  Eng.  News,  Vol.  33,  p.  341. 

ASHLAND,  WlS.  Designed  by  William  Wheeler,  built  in  1895. 
The  Ashland  filters  were  the  first  vaulted  masonry  filters  to  be  con- 
structed in  the  United  States,  and  are  used  for  treating  the  bay 
water,  which  is  polluted  with  sewage,  and  is  at  times  muddy  from  the 
river  water  discharging  into  the  bay  near  the  intake.  The  filters  are 
below  the  bay  level,  and  receive  water  from  it  by  gravity.  Descrip- 
tion :  Jour.  N.  E.  Water  Works  Assoc.,  Vol.  11,  p.  301  ;  Eng.  News, 
Vol.  38,  p.  338. 

LAMBERTSVILLE,  N.  J.     Designed  by  Churchill  Hungerford,  and 


APPENDIX  IV.  253 

built  in  1896.  These  are  open  filters  with  earth  embankments,  for 
filtration  of  reservoir  water.  Description  :  Eng.  News,  Vol.  361 
p.  4. 

FAR  ROCKAWAY,  L.  I.  (Queen's  County  Water  Company.) 
Designed  by  C.  B.  Brush  &  Co.,  with  Allen  Hazen  as  Consulting 
Engineer,  and  were  constucted  in  1896;  Charles  R.  Bettes,  Construct- 
ing Engineer.  These  masonry  filters  are  used  for  the  removal  of  iron 
from  well  waters.  They  are  also  designed  to  be  suitable  for  the 
filtration  of  certain  brook  waters  which  are  available  as  auxiliary 
supplies,  but  the  brook  water  has  been  but  rarely  used.  Descrip- 
tion :  Eng.  Record,  Vol.  40,  p.  412. 

RED  BANK,  N.  J.  (Rumson  Improvement  Company.)  Designed 
by  Allen  Hazen,  built  in  1897.  They  are  similar  in  construction  to 
the  Far  Rockaway  filters,  and  are  used  for  iron  removal  only.  De- 
scription :  Eng.  Record,  Vol.  40,  p.  412. 

HAMILTON,  N.  Y.  Designed  by  the  Stanwix  Engineering  Com- 
pany, and  were  built  in  1895  to  filter  lake  water.  Description:  Eng. 
News,  Vol.  39,  p.  254. 

LITTLE  FALLS,  N.  Y.  Designed  by  Stephen  E.  Babcock.  These 
filters  are  open,  and  were  built  in  1898,  and  are  used  for  filtering 
river  water.  Description  :  Eng.  Record,  Vol.  38,  p.  7. 

SOMERSWORTH,  N.  H.  Designed  by  William  Wheeler.  These 
were  the  second  vaulted  filters  to  be  built  in  the  United  States. 
The  supply  is  from  the  Salmon  Falls  River  and  flows  to  the  filters 
by  gravity,  the  filters  being  below  the  river  level.  Description : 
Eng.  News,  Vol  40,  p.  358 ;  Eng.  Record,  Vol.  38,  p.  270. 

BERWYN,  PENNA.  Designed  by  J.  W.  Ledoux.  These  open 
filters  are  used  for  filtering  creek  water.  Description  :  Eng.  News, 
Vol.  41,  p.  150. 

HARRISBURG,  PENNA.  (State  Lunatic  Hospital.)  Designed  by 
Allen  Hazen  ;  open  masonry  filters,  used  for  treating  the  water  from 
a  small  creek  which  is  often  muddy  and  is  subject  to  pollution.  No 
published  description. 


254  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

ALBANY,  N.  Y.  Designed  by  Allen  Hazen.  Constructed  1898-99. 
This  was  the  third  and  is  the  largest  vaulted  masonry  filter  plant  yet 
constructed  in  the  United  States.  It  is  used  for  filtering  the  Hudson 
River  water,  which  is  slightly  muddy  and  much  polluted  by  sewage. 
Description  :  Eng.  News,  Vol.  39,  p.  91  ;  Vol.  40,  p.  254. 

ROCK  ISLAND,  ILL.  Designed  by  Jacob  A.  Harman.  Open 
filters  with  embankments,  used  for  filtering  the  Mississippi  River 
water,  which  is  very  muddy  and  also  polluted  by  sewage.  No 
published  description. 


CAPACITY    OF   FILTERS. 

Estimating  the  total  additional  area"  of  sand  filters  for  which 
figures  are  not  available  at  100  acres,  and  the  maximum  capacity 
of  sand  filters  at  three  million  gallons  per  acre  daily,  and  of  me- 
chanical filters  at  three  million  gallons  per  thousand  square  feet  of 
filtering  area,  the  total  filtering  capacity  of  all  the  filters  in  the 
world  used  for  public  water  supplies  in  1899  is  nearly  1600  million 
gallons  daily,  of  which  15  per  cent  is  represented  by  mechanical 
filters  and  85  per  cent  by  sand  filters.  In  the  United  States,  in- 
cluding Wilmington,  the  total  filtering  capacity  is  nearly  300  million 
gallons  daily,  of  which  18  per  cent  is  represented  by  sand  filters,  79 
per  cent  by  mechanical  filters,  and  3  per  cent  by  a  special  type  of 
filters. 


APPENDIX    V.  255 


APPENDIX  V. 
LONDON'S   WATER-SUPPLY. 

LONDON  alone  among  great  capitals  is  supplied  with  water  by 
private  companies.  They  are,  however,  under  government  super- 
vision, and  the  rates  charged  for  water  are  regulated  by  law.  There 
are  eight  companies,  each  of  which  supplies  its  own  separate  dis- 
trict, so  that  there  is  no  competition  whatever.  One  of  the  compa- 
nies supplying  460,000  people  uses  only  ground-water  drawn  from 
deep  wells  in  the  chalk,  but  the  other  seven  companies  depend 
mainly  upon  the  rivers  Thames  and  Lea  for  their  water.  All 
water  so  drawn  is  filtered,  and  must  be  satisfactory  to  the  water 
examiner,  who  is  required  to  inspect  the  water  supplied  by  each 
company  at  frequent  intervals,  and  the  results  of  the  examinations 
are  published  each  month. 

In  1893  the  average  daily  supply  was  235,000,000  gallons,  of 
which  about  40,000,000  were  drawn  from  the  chalk,  125,000,000 
from  the  Thames,  and  70,000,000  from  the  Lea.  Formerly  some  of 
the  water  companies  drew  water  from  the  Thames  within  the  city 
where  it  was  grossly  polluted,  and  the  plagues  and  cholera  which 
formerly  ravaged  London  were  in  part  due  to  this  fact.  These 
intakes  were  abandoned  many  years  ago,  and  all  the  companies 
now  draw  their  water  from  points  outside  of  the  city  and  its  imme- 
diate suburbs. 

The  area  of  the  watershed  of  the  Thames  above  the  intakes  of 
the  water  companies  is  3548  square  miles,  and  the  population  living 
upon  it  in  1891  was  1,056,415.  The  Thames  Conservancy  Board 
has  control  of  the  main  river  for  its  whole  length,  and  of  all  tributa- 
ries within  ten  miles  in  a  straight  line  of  the  main  river,  but  has  no 


256  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

jurisdiction  over  the  more  remote  feeders.  The  area  drained  is 
essentially  agricultural,  with  but  little  manufacturing,  and  there  are 
but  few  large  towns.  In  the  area  coming  under  the  conservators 
there  are  but  six  towns  with  populations  above  10,000  and  an  aggre- 
gate population  of  170,000,  and  there  are  but  two  or  three  other 
large  towns  on  the  remaining  area  more  than  ten  miles  from  the 
river.  These  principal  towns  are  as  follows  : 


Town.  Population  ,8,,. 

Reading   ..................  60,054  49  miles 

Oxford  ....................  45,791  87  " 

New  Swindon  .........  .  ----  27,295  116  " 

HighWycomb  .............  13,435  33  " 

Windsor  ...................  12,327  18  " 

Maidenhead  ...............  10,607  25  " 

Guildford  ...................  14.319  20  " 

Guildford  is  outside  of  the  conservators'  area.  All  of  the  above 
towns  treat  their  sewage  by  irrigation. 

Among  the  places  that  are  regarded  as  the  most  dangerous  are 
Chertsey  and  Staines,  with  populations  of  9215  and  5060,  only  8  and 
II  miles  above  the  intakes  respectively.  These  towns  are  only 
partially  sewered  and  still  depend  mainly  on  cesspools.  An  at- 
tempt is  made  to  treat  the  little  sewage  which  they  produce  upon 
land,  but  the  work  has  not  as  yet  been  systematically  carried  out. 
There  are  also  several  small  towns  of  3000  inhabitants  or  less  upon 
the  upper  river  which  do  not  treat  their  sewage  so  far  as  they 
have  any,  but,  owing  to  their  great  distance,  the  danger  from  them 
is  much  less  than  from  Chertsey  and  Staines.  Twenty-one  of  the 
principal  towns  upon  the  watershed  have  sewage  farms,  and  there 
are  no  chemical  precipitation  plants  now  in  use. 

Boats  upon  the  river  are  not  allowed  to  drain  into  it,  but  are 
compelled  to  provide  receptacles  for  their  sewage,  and  facilities  are 
provided  for  removing  and  disposing  of  it  ;  and  as  an  additional  pre- 
caution no  boat  is  allowed  to  anchor  within  five  miles  of  the  in- 
takes. 


APPENDIX    V.  257 

The  conservators  of  the  river  Lea  have  control  of  its  entire 
drainage  area,  which  is  about  460  square  miles,  measured  from  the 
East  London  water  intakes,  and  has  a  population  of  189,287.  On 
this  watershed  there  is  but  a  single  town  with  more  than  10,000  in- 
habitants, this  being  Lutton  near  the  headwaters  of  the  river,  with  a 
population  of  30,005.  The  sewage  from  Lutton  and  from  seven- 
teen smaller  places  is  treated  upon  land.  No  crude  sewage  is 
known  to  be  ordinarily  discharged  into  the  river.  At  Hereford, 
eleven  miles  above  the  East  London  intakes,  there  is  a  chemical 
precipitation  plant.  The  conservators  do  not  regard  this  treatment 
as  satisfactory,  and  have  recently  conducted  an  expensive  lawsuit 
against  the  local  authorities  to  compel  them  to  further  treat  their 
effluent.  The  suit  was  lost,  the  court  holding  that  no  actual  injury 
to  health  had  been  shown.  It  is  especially  interesting  to  note  that 
of  the  thirty-nine  places  on  the  Thames  and  the  Lea  giving  their 
sewage  systematic  treatment  there  is  but  a  single  place  using  chem- 
ical precipitation,  and  there  it  is  not  considered  satisfactory.  Form- 
erly quite  a  number  of  these  towns  used  other  processes  than  land 
treatment,  but  in  every  case  but  Hereford  land  treatment  has  been 
substituted. 

In  regard  to  the  efficiency  of  the  sewage  farms,  it  is  believed 
that  in  ordinary  weather  the  whole  of  the  sewage  percolates 
through  the  land,  and  the  inspectors  of  the  Conservancy  Boards 
strongly  object  to  its  being  allowed  to  pass  over  the  surface  into 
the  streams.  The  land,  however,  is  for  the  most  part  impervious, 
as  compared  to  Massachusetts  and  German  sewage  farms,  and  in 
times  of  heavy  storms  the  land  often  has  all  the  water  it  can  take 
without  receiving  even  the  ordinary  flow  of  sewage,  and  much  less 
the  increased  storm-flow.  At  such  times  the  sewage  either  does  go 
over  the  surface,  or  perhaps  more  frequently  is  discharged  directly 
into  the  rivers  without  even  a  pretence  of  treatment.  The  con- 
servators apparently  regard  this  as  an  unavoidable  evil  and  do  not 
vigorously  oppose  it.  It  is  the  theory  that,  owing  to  the  increased 
dilution  with  the  storm-flows,  the  matter  is  comparatively  harmless, 


2$ 8  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

although  it  would  seem  that  the  reduced  time  required  for  it  to 
reach  the  water-works  intakes  might  largely  offset  the  effect  of 
increased  dilution. 

The  water  companies  have  large  storage  and  sedimentation 
basins  with  an  aggregate  capacity  equal  to  nine  days'  supply,  but 
the  proportion  varies  widely  with  the  different  companies.  It  is 
desired  that  the  water  held  in  reserve  shall  be  alone  used  while  the 
river  is  in  flood,  as,  owing  to  its  increased  pollution,  it  is  regarded 
as  far  more  dangerous  than  the  water  at  other  times;  but  as  no 
record  is  kept  of  the  times  when  raw  sewage  is  discharged,  and  no 
exact  information  is  available  in  regard  to  the  times  when  the  com- 
panies do  not  take  in  raw  water,  it  can  safely  be  assumed  that  a 
considerable  amount  of  raw  sewage  does  become  mixed  with  the 
water  which  is  drawn  by  the  companies. 

The  water  drawn  from  the  river  is  filtered  through  113  filters 
having  an  area  of  116  acres.  None  of  the  filters  are  covered,  and 
with  an  average  January  temperature  of  39°  but  little  trouble  with 
ice  is  experienced.  A  few  new  filters  are  provided  with  appliances 
for  regulating  the  rate  on  each  filter  separately  and  securing  regular 
and  determined  rates  of  filtration,  but  nearly  all  of  the  filters  are  of 
the  simple  type  described  on  page  48,  and  the  rates  of  filtration 
are  subject  to  more  or  less  violent  fluctuation,  the  extent  of  which 
cannot  be  determined. 

The  area  of  filters  is  being  continually  increased  to  meet  increas- 
ing consumption  ;  the  approximate  areas  of  filters  in  use  having 
been  as  follows : 

1839 First  filters  built 

1855 37  acres 

1866 47     " 

1876 77     " 

1886 104     " 

1894 116     " 

There  has  been  a  tendency  to  reduce  somewhat  the  rate  of  filtra 
tion.     In  1868,  with  51  acres  of  filters,  the  average  daily  quantity  of 


APPENDIX    V.  259 

water  filtered  was  111,000,000  gallons,  or  2,180,000  gallons  per  acre. 
In  1884,  witn  97  acres  of  filter  surface,  the  daily  quantity  filtered  was 
157,000,000  gallons,  or  1,620,000  gallons  per  acre  ;  and  in  1893,  with 
1 1 6  acres  of  filter  surface  and  195,000,000  gallons  daily,  the  yield 
per  acre  was  1,680,000  gallons. 

Owing  to  the  area  of  filter  surface  out  of  use  while  being  cleaned, 
the  variations  in  consumption  of  water,  and  the  imperfections  of  the 
regulating  apparatus,  the  actual  rates  of  filtration  are  often  very 
much  higher  and  at  times  may  easily  be  double  the  figures  given. 

Evidence  regarding  the  healthfulness  of  the  filtered  river-water 
was  collected  and  examined  in  a  most  exhaustive  manner  in  1893 
by  a  Royal  Commission  appointed  to  consider  the  water-supply  of 
the  metropolis  in  all  its  aspects  with  reference  to  future  needs.  This 
commission  was  unable  to  obtain  any  evidence  whatever  that  the 
water  as  then  supplied  was  unhealthy  or  likely  to  become  so,  and 
they  report  that  the  rivers  can  safely  be  depended  upon  for  manjr 
years  to  come. 

The  numbers  of  deaths  from  all  causes  and  from  typhoid  fever 
annually  per  million  of  inhabitants  for  the  years  1885-1891  in  the 
populations  receiving  their  waters  from  different  sources  in  London 
were  as  follows : 

w  ,  Deaths  from          Deaths  from 

All  Causes.       Typhoid  Fever. 
Filtered  Thames  water  only 19*501  125 

Lea  water  only 21,334  167 

Kent  wells  only 18,001  123 

Thames  and  Lea  jointly 18,945  138 

"     Kent  jointly 18,577  133 

The  population  supplied  exclusively  from  the  Lea  by  the  East 
London  Company  is  of  a  poorer  class  than  that  of  the  rest  of  Lon- 
don, and  this  may  account  for  the  slightly  higher  death-rate  in  this 
section.  Aside  from  this  the  rate  is  remarkably  uniform  and  shows 
no  great  difference  between  the  section  drinking  ground-water  only 
and  those  drinking  filtered  river-waters.  The  death-rate  from 


260 


FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


typhoid  fever  is  also  very  uniform  and,  although  higher  than  that  of 
some  Continental  cities  with  excellent  water-supplies  (Berlin,  Vienna, 
Munich,  Dresden),  is  very  low — lower  than  in  any  American  city  of 
which  I  have  records. 

In  this  connection,  it  was  shown  by  the  Registrar-General  that 
there  is  only  a  very  small  amount  of  typhoid  fever  on  the  water- 
sheds of  the  Thames  and  Lea,  so  that  the  danger  of  infection  of  the 
water  as  distinct  from  pollution  is  less  than  would  otherwise  be  the 
case.  Thus  for  the  seven  years  above  mentioned  the  numbers  of 
deaths  from  typhoid  fever  per  million  of  population  were  only  105 
and  120  on  the  watersheds  of  the  Thames  and  the  Lea  respectively, 
as  against  176  for  the  whole  of  England  and  Wales. 


LONDON   FILTERS,    1896. 
Twenty-sixth  Annual  Report  of  the  Local  Government  Board,  pages  206-213. 


1 

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APPENDIX    VI.  26l 


APPENDIX    VI. 
THE  BERLIN  WATER-WORKS. 

THE  original  works  were  built  by  an  English  company  in  1856, 
and  were  sold  to  the  city  in  1873  for  $7,200,000. 

The  water  was  taken  from  the  river  Spree  at  the  Stralau  Gate, 
which  was  then  above,  but  is  now  surrounded  by,  the  growing  city. 
The  water  was  always  filtered,  and  the  original  filters  remained  in  use 
until  1893,  when  they  were  supplanted  by  the  new  works  at  Lake 
Miiggel.  Soon  after  acquiring  the  works  the  city  introduced  water 
from  wells  by  Lake  Tegel  as  a  supplementary  supply,  but  much 
trouble  was  experienced  from  crenothrix,  an  organism  growing  in 
ground-waters  containing  iron,  and  in  1883  this  supply  was  replaced 
by  filtered  water  from  Lake  Tegel.  With  rapidly-increasing  pollu- 
tion of  the  Spree  at  Stralau  the  purity  of  this  source  was  questioned, 
and  in  1893  it  was  abandoned  (although  still  held  as  a  reserve  in  case 
of  urgent  necessity),  the  supply  now  being  taken  from  the  river  ten 
miles  higher  up,  at  Miiggel. 

The  watershed  of  the  Spree  above  Stralau,  as  I  found  by  map 
measurement,  is  about  3800  square  miles ;  the  average  rainfall  is 
about  25  inches  yearly.  At  extreme  low  water  the  river  discharges 
457  cubic  feet  per  second,  or  295  million  gallons  daily,  and  when  in 
flood  5700  cubic  feet  per  second  may  be  discharged.  The  city  is 
allowed  by  law  to  take  46  million  gallons  daily  for  water-supply,  and 
this  quantity  can  be  drawn  either  at  Stralau  or  at  Miiggel. 

Above  Stralau  the  river  is  polluted  by  numerous  manufactories 
and  washing  establishments,  and  by  the  effluent  from  a  considerable 
part  of  the  city's  extensive  sewage  farms.  The  shipping  on  this 
part  of  the  river  also  is  heavy,  and  sewage  from  the  boats  is  dis- 


262  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

charged  directly  into  the  river.  The  average  number  of  bacteria  in 
the  Spree  at  this  point  is  something  over  ten  thousand  per  cubic 
centimeter,  and  99.6  per  cent  of  them  were  removed  by  the  filters 
in  1893. 

The  watershed  of  the  Spree  above  the  new  water-works  at 
Miiggel  I  found  by  map  measurement  to  be  2800  square  miles,  and 
the  low  water-discharge  is  said  to  be  269  million  gallons  daily.  The 
river  at  this  point  flows  through  Lake  Miiggel,  which  forms  a  natural 
sedimentation-basin,  and  the  raw  water  is  quite  clear  except  in  windy 
weather. 

There  were  16  towns  on  the  watershed  with  populations  above 
2000  each  in  1890,  and  an  aggregate  population  of  132,000,  which 
does  not  include  the  population  of  the  smaller  places  or  country 
districts.  None  of  these  places  purify  their  sewage  so  far  as 
they  have  any.  Furstenwalde  with  a  population  of  12,935,  and 
22  miles  above  Miiggel,  has  surface  sewers  discharging  directly  into 
the  river.  Above  Furstenwalde  the  river  runs  through  numerous 
lakes  which  probably  remove  the  effect  of  the  pollution  from  the  more 
distant  cities.  There  is  considerable  shipping  on  the  river  for  some 
miles  above  Furstenwalde  (which  forms  a  section  of  the  Friedrich 
Wilhelm  Canal),  but  hardly  any  between  Mtiggel  and  Furstenwalde. 
The  raw  water  at  Muggel  contains  two  or  three  hundred  bacteria 
per  cubic  centimeter,  and  is  thus  a  comparatively  pure  water  before 
filtration.  It  is  slightly  peaty  and  the  filtered  water  has  a  light  straw 
color. 

Lake  Tegel,  which  supplies  the  other  part  of  the  city's  supply,  is 
an  enlargement  of  the  river  Havel.  The  watershed  above  Tegel 
I  find  to  be  about  1350  square  miles,  and  the  annual  rainfall  is 
about  22  inches.  The  low  water-discharge  is  said  to  be  182  million 
gallons  daily,  and  the  city  is  allowed  by  law  to  take  23  million  gal- 
lons for  water-supply. 

There  were  ten  towns  upon  the  watershed  with  populations 
above  2000  each  in  1890,  and  with  an  aggregate  population  of  44,000. 
Of  these  Tegel  is  directly  upon  the  lake  with  a  population  of  3000, 


APPENDIX    VI.  263 

and  Oranienburg,  14  miles  above,  has  a  population  of  6000  and  is 
rapidly  increasing.  The  shipping  on  the  lake  and  river  is  heavy. 
The  lake  water  ordinarily  contains  two  or  three  hundred  bacteria 
per  cubic  centimeter.  The  lake  is  shallow  and  becomes  turbid  in 
windy  weather. 

There  are  21  filter-beds  at  Tegel  with  a  combined  area  of  12.40 
acres  to  furnish  a  maximum  of  23  million  gallons  of  water  daily, 
and  22  filters  at  Miiggel  with  a  combined  area  of  12.7  acres  to  de- 
liver the  same  quantity.  Twenty-two  more  filters  will  be  built  at 
Miiggel  within  a  few  years  to  purify  the  full  quantity  which  can  be 
taken  from  the  river.  All  of  these  filters  are  covered  with  brick 
arches  supported  by  pillars  about  16  feet  apart  from  centre  to  centre 
in  each  direction,  and  the  whole  is  covered  by  nearly  3  feet  of  earth, 
making  them  quite  frost-proof.  The  original  filters  at  Stralau  were 
open,  but  much  difficulty  was  experienced  with  them  in  winter. 

The  bottom  of  the  filters  at  Tegel  consists  of  8  inches  of  concrete 
above  20  inches  of  packed  clay  and  with  2  inches  of  cement  above, 
and  slopes  slightly  from  each  side  to  the  centre.  The  central  drain 
goes  the  whole  length  of  the  filters  and  has  a  uniform  cross-section 
of  about  73100  of  the  area  of  the  whole  bed.  There  are  no  lateral 
drains,  but  the  water  is  brought  to  the  central  drain  by  a  twelve- 
inch  layer  of  stones  as  large  as  a  man's  fist ;  above  this  there  is  an- 
other foot  of  gravel  of  graded  sizes  supporting  two  feet  of  fine  sand, 
which  is  reduced  by  scraping  to  half  its  thickness  before  the  sand  is 
replaced.  The  average  depth  of  water  above  the  sand  is  nearly  5  feet. 
The  filters  are  not  allowed  to  filter  at  a  rate  above  2.57  million  gal- 
lons per  acre  daily,  and  at  this  rate  with  70  per  cent  of  the  area  in 
service  the  whole  legal  quantity  of  water  can  be  filtered.  The  filters 
work  at  precisely  the  same  rate  day  and  night,  and  the  filtered  water 
is  continuously  pumped  as  filtered  to  ample  storage  reservoirs  at 
Charlottenburg.  The  pumps  which  lift  the  water  from  the  lake  to 
the  filters  work  against  a  head  of  14  feet.  The  apparatus  for  regu- 
lating the  rate  of  filtration  was  described  on  page  51. 

As  yet  no  full  description  of  the  Miiggel  works  has  been  pub- 


264  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

lished,  but  they  resemble  closely  the  Tegel  works.  Both  were  de- 
signed by  or  under  the  direction  of  the  late  director  of  the  water- 
works, Mr.  Henry  Gill. 

The  average  daily  quantity  of  water  supplied  for  the  fiscal 
year  ending  March  31,  1893,  was  29,000,000  gallons  daily,  which  es- 
timate allows  10  per  cent  for  the  slip  of  the  pumps.  Of  this  quan- 
tity 9,650,000  was  furnished  by  Stralau  and  19,350,000  by  Tegel. 
The  greatest  consumption  in  a  single  day  was  43,300,000  gallons,  or 
26.6  gallons  per  head,  while  the  average  quantity  for  the  year  was 
18.4  gallons  per  head.  All  water  without  exception  is  sold  by  meter, 
the  prices  ranging  from  27.2  cents  a  thousand  gallons  for  small  con- 
sumers to  13.6  cents  for  large  consumers  and  manufacturers.  The 
average  receipts  for  all  water  pumped,  including  that  used  for  pub- 
lic purposes  and  not  paid  for,  were  15.4  cents  a  thousand  gallons, 
against  the  cost  of  production,  9.8  cents,  which  covers  operating  ex- 
penses, interest  on  capital,  and  provision  for  sinking  fund.  This 
leaves  a  handsome  net  profit  to  the  city.  On  account  of  the  com- 
paratively high  price  of  the  city  water  and  the  ease  with  which  well- 
water  is  obtained,  the  latter  is  almost  exclusively  used  for  running 
engines,  manufacturing  purposes,  etc.,  and  this  in  part  explains  the 
very  low  per-capita  consumption. 

The  volume  of  sewage,  however,  for  the  same  year,  including 
rain-water,  except  during  heavy  showers,  was  only  29  gallons  per 
head,  showing  even  with  the  private  water-supplies  an  extraordi- 
narily low  consumption. 

The  friction  of  the  water  in  the  4.75  miles  of  3-foot  pipe  between 
Tegel  and  the  reservoir  at  Charlottenburg  presents  an  interesting 
point.  When  well-water  with  crenothrix  was  pumped,  the  friction  rose 
to  34. 5  feet,  when  the  velocity  was  2.46  feet  per  second.  According  to 
Herr  Anklamm,  who  had  charge  of  the  works  at  the  time,  the  friction 
was  reduced  to  19.7  feet  when  filtered  water  was  used  and  after  the 
pipe  had  been  flushed,  and  this  has  not  increased  with  continued 
use.  He  calculated  the  friction  for  the  velocity  according  to  Darcy 
15.0  feet,  Lampe  17.8  feet,  Weisbach  18.7  feet,  and  Prony  21.5  feet^ 


APPENDIX    VII.  265 


APPENDIX  VII. 
ALTONA  WATER-WORKS. 

THE  Altona  water-works  are  specially  interesting  as  an  example 
of  a  water  drawn  from  a  source  polluted  to  a  most  unusual  extent : 
the  sewage  from  cities  with  a  population  of  770,000,  including  its 
own,  is  discharged  into  the  river  Elbe  within  ten  miles  above  the 
intake  and  upon  the  same  side. 

The  area  of  the  watershed  of  the  Elbe  above  Altona  is  about 
52,000  square  miles,  and  the  average  rainfall  is  estimated  to  be 
about  28  inches,  varying  from  24  or  less  near  its  mouth  to  much 
higher  quantities  in  the  mountains  far  to  the  south.  On  this  water- 
shed there  are  46  cities,  which  in  1890  had  populations  of  over  20,000 
each,  and  in  addition  there  is  a  permanent  population  upon  the  river- 
boats  estimated  at  20,000,  making  in  all  5,894,000  inhabitants,  with- 
out including  either  country  districts  or  the  numberless  cities  with 
less  than  20,000  inhabitants  each.  The  sewage  from  about  1,700,000 
of  these  people  is  purified  before  being  discharged  ;  and  assuming 
that  as  many  people  living  in  cities  smaller  than  20,000  are  con- 
nected with  sewers  as  live  in  larger  places  without  being  so  con- 
nected, the  sewage  of  over  four  million  people  is  discharged 
untreated  into  the  Elbe  and  its  tributaries. 

The  more  important  of  these  sources  of  pollution  are  the  fol- 
lowing : 

Ci  Population  On  what     Approximate 

in  1890.  River.    Distance,  Miles 

Shipping 20,000 


Altona !43»353  Elbe  6 

Hamburg 570,534  "  7 

\Yandsbeck 20,586  "  8 


266  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

~.  Population  On  what      Approximate 

in  1890.  River.     Distance,  Miles. 

Harburg 35>ioi  Elbe  11 

Magdeburg 202,325               "  185 

Dresden 276,085               "  354 

Berlin  and  suburbs 1,787,859  Havel  243 

Halle 101,401  Saale  272 

Leipzig 355485  Elster  305 

Chemnitz 138,955  Mulde  340 

Prague 310,483  Moldau  500 

The  sewage  of  Berlin  and  of  most  of  its  suburbs  is  treated  before 
being  discharged,  and  in  addition  the  Havel  flows  through  a  series 
of  lakes  below  the  city,  allowing  better  opportunities  for  natural 
purification  than  in  the  case  of  any  of  the  other  cities.  Halle  treats 
less  than  a  tenth  of  its  sewage.  Magdeburg  will  treat  its  sewage  in 
the  course  of  a  few  years.  Leipzig,  Chemnitz,  and  other  places  are 
thinking  more  or  less  seriously  of  purification. 

The  number  of  bacteria  in  the  raw  water  at  Altona  fluctuates 
with  the  tide  and  is  extremely  variable;  numbers  of  50,000  and 
100,000  are  not  infrequent,  but  10,000  to  40,000  is  perhaps  about 
the  usual  range. 

The  works  were  originally  built  by  an  English  company  in  1860, 
and  have  since  been  greatly  extended.  They  were  bought  by  the 
city  some  years  ago.  The  water  is  pumped  directly  from  the  river 
to  a  settling-basin  upon  a  hill  280  feet  above  the  river.  From  this 
it  flows  by  gravity  through  the  filters  to  the  slightly  lower  pure- 
water  reservoir  and  to  the  city  without  further  pumping.  The 
filters  are  open,  with  nearly  vertical  masonry  walls,  as  described  in 
Kirkwood's  report.  The  cross-section  of  the  main  underdrain  is 
3-5*3-5-  of  the  area  of  the  beds. 

Considerable  trouble  has  been  experienced  from  frost.  With 
continued  cold  weather  it  is  extremely  difficult  to  satisfactorily 
scrape  the  filters,  and  very  irregular  rates  of  filtration  may  result 
at  such  times.  In  the  last  few  years,  with  systematic  bacterial 
investigation,  it  has  been  found  that  greatly  decreased  efficiency 


APPENDIX    VII.  267 

frequently  follows  continued  cold  weather,  and  the  mild  epidemics 
of  typhoid  fever  from  which  the  city  has  long  suffered  have 
generally  occurred  after  these  times.  Thus  a  light  epidemic  of 
typhoid  in  1886  came  in  March,  following  a  light  epidemic  in 
Hamburg.  In  1887  a  severe  epidemic  in  February  followed  a 
severe  epidemic  in  Hamburg  in  December  and  January.  In  1888 
a  severe  epidemic  in  March  followed  an  epidemic  in  Hamburg 
lasting  from  November  to  January.  Hamburg's  epidemic  of 
1889,  coming  in  warm  weather,  September  and  October,  was  fol- 
lowed by  only  a  very  slight  increase  in  Altona.  In  1891  Altona 
suffered  again  in  February  from  a  severe  epidemic,  although  very 
little  typhoid  had  been  in  Hamburg.  A  less  severe  outreak  also 
came  in  February,  1892,  and  a  still  slighter  one  in  February,  1893. 
In  the  ten  years  1882-1892,  of  five  well-marked  epidemics,  three 
broke  out  in  February  and  two  in  March,  while  two  smaller  out- 
breaks came  in  December  and  January.  No  important  outbreak 
has  ever  occurred  in  summer  or  in  the  fall  months,  when  typhoid  is 
usually  most  prevalent,  thus  showing  clearly  the  bad  effect  of  frost 
upon  open  filters  (see  Appendix  II).  With  steadily  increasing 
consumption  the  sedimentation-basin  capacity  of  late  years  has 
become  insufficient  as  well  as  the  filtering  area,  and  it  is  not  unlikely 
that  with  better  conditions  a  much  better  result  could  be  obtained 
in  winter  even  with  open  filters.* 

The  brilliant  achievement  of  the  Altona  filters  was  in  the  sum- 
mer of  1892,  when  they  protected  the  city  from  the  cholera  which 

*  In  the  Ctntralblatt  fur  Bakteriologie >  1895,  page  88 1,  Reinsch  discusses  at  length 
the  cause  of  the  inferior  results  at  Altona  in  winter,  and  has  apparently  discovered  a 
new  factor  in  producing  them.  Owing  to  defective  construction  of  the  outlets  for  the 
sedimentation-basins  they  have  failed  to  act  properly  in  presence  of  excessive  quantities 
of  ice,  and  the  sediment  from  the  basins  has  been  discharged  in  large  quantity  upon 
the  filters,  and  a  small  fraction  of  the  many  millions  of  bacteria  in  it  have  passed 
through  the  filters.  He  has  experimented  with  this  sediment  applied  to  small  filters, 
and  has  become  convinced  that  to  secure  good  work  under  all  conditions  a  much  deeper 
layer  of  sand  than  that  generally  considered  necessary  must  be  used,  and  his  work 
emphasizes  the  importance  of  the  action  of  the  sand  in  distinction  from  the  action  of 
the  sediment  layer,  which  has  often  been  thought  to  be  the  sole,  or  at  least  the  princi- 
pal, requirement  of  good  filtration. 


268  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 

so  ravaged  Hamburg,  although  the  raw  water  at  Altona  must  have 
contained  a  vastly  greater  quantity  of  infectious  matter  than  that 
which  worked  such  havoc  in  Hamburg. 

From  these  records  it  appears  that  for  about  nine  months  of  the 
year  the  Altona  filters  protect  the  city  from  the  impurities  of  the 
Elbe  water,  but  that  during  cold  weather,  with  continued  mean 
temperatures  below  the  freezing-point,  such  protection  is  not  com- 
pletely afforded,  and  bad  effects  have  occasionally  resulted.  Not- 
withstanding the  recent  construction  of  open  filters  in  Hamburg  it 
appears  to  me  that  there  must  always  be  more  or  less  danger  from 
open  filters  in  such  a  climate.  Hamburg's  danger,  however,  will  be 
much  less  than  Altona's  on  account  of  its  better  intake  above  the 
outlets  of  the  sewers  of  Hamburg  and  Altona,  which  are  the  most 
important  points  of  pollution  at  Altona. 


APPENDIX    VIII.  269 


APPENDIX    VIII. 
HAMBURG  WATER-WORKS. 

THE  source  and  quality  of  the  water  previously  supplied  has  been 
sufficiently  indicated  in  Appendix  II.  It  was  originally  intended 
to  filter  the  water,  but  the  construction  of  filters  was  postponed 
from  time  to  time  until  the  fall  of  1890,  when  the  project  was 
seriously  taken  up,  and  work  was  commenced  in  the  spring  of  1891. 
Three  years  were  allowed  for  construction.  In  1892,  however,  the 
epidemic  of  cholera  came,  killing  8605  residents  and  doing  incalcu- 
lable damage  to  the  business  interests  of  the  city.  The  health 
authorities  found  that  the  principal  cause  of  this  epidemic  was  the 
polluted  water-supply.  To  prevent  a  possible  recurrence  of  cholera 
in  1893,  the  work  of  construction  of  the  filters  was  pressed  forward 
much  more  rapidly  than  had  been  intended.  Electric  lights  were 
provided  to  allow  the  work  to  proceed  nights  as  well  as  days,  and 
as  a  result  the  plant  was  put  in  operation  May  27,  1893,  a  full  year 
before  the  intended  time.  Owing  to  the  forced  construction  the 
cost  was  materially  increased. 

The  new  works  take  the  raw  water  from  a  point  one  and  a  half 
miles  farther  up-stream,  where  it  is  believed  the  tide  can  never  carry 
the  city's  own  sewage,  as  it  did  frequently  to  the  old  intake. 
The  water  is  pumped  from  the  river  to  settling-basins  against  heads 
varying  with  tide  and  the  water-level  in  the  basins  from  8  to  22 
feet.  Each  of  the  four  settling-basins  has  an  area  of  about  10 
acres,  and,  with  the  water  6.56  feet  deep,  holds  20,500,000  gallons, 
or  82,000,000  gallons  in  all.  The  works  are  intended  to  supply  a 
maximum  of  48,000,000  gallons  daily,  but  the  present  average  con- 
sumption is  only  about  35,000,000  gallons  (1892),  or  59  gallons  per 


270  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

head  for  600,000  population.  This  consumption  is  regarded  as  ex 
cessive,  and  it  is  hoped  that  it  will  be  reduced  materially  by  the  more 
general  use  of  meters.  The  sedimentation-basins  are  surrounded  by 
earthen  embankments  with  slopes  of  1:3,  the  inner  sides  being  paved 
with  brick  above  a  clay  layer.  The  water  flows  by  gravity  from 
these  basins  to  the  filters,  a  distance  of  i£  miles,  through  a  conduit 
8£  feet  in  diameter.  The  flow  of  the  water  out  of  the  basins  and 
from  the  lower  end  of  the  conduit  is  regulated  by  automatic  gates 
connected  with  floats,  shown  by  Fig.  n,  page  56. 

The  filters  are  18  in  number,  and  each  has  an  effective  area 
of  1.89,  or  34  acres  in  all.  They  are  planned  to  filter  at  a  rate 
of  i. 60  million  gallons  per  acre  daily,  which  with  16  filters  in  use 
gives  a  daily  quantity  of  48,000,000  gallons  as  the  present  limit  of 
the  works.  The  sides  of  the  filters  are  embankments  with  I  :  2 
slopes.  Both  sides  and  bottoms  have  20  inches  of  packed  clay, 
above  which  are  4  inches  of  puddle,  supporting  a  brick  pavement 
laid  in  cement.  The  bricks  are  laid  flat  on  the  bottom,  but  edge- 
wise on  the  sides  where  they  will  come  in  contact  with  ice. 

The  main  effluent-drain  has  a  cross-section  for  the  whole  length 
of  the  filter  of  4.73  square  feet,  or  TTJo^-  of  the  area  of  the  filter;  and 
even  at  the  low  rate  of  filtration  proposed,  the  velocity  in  the  drain 
will  reach  0.97  foot.  The  drain  has  brick  sides,  1.80  feet  high,  cov- 
ered with  granite  slabs.  The  lateral  drains  are  all  of  brick  with 
numerous  large  openings  for  admission  of  water.  They  are  not 
ventilated,  and  I  am  unable  to  learn  that  any  bad  results  follow 
this  omission. 

The  filling  of  the  filters  consists  of  2  feet  of  gravel,  the  top 
being  of  course  finer  than  the  bottom  layers,  above  which  are  40 
inches  of  sand,  which  are  to  be  reduced  to  24  inches  by  scraping 
before  being  refilled.  The  water  over  the  sand,  when  the  latter  is  of 
full  depth,  is  43  inches  deep,  and  will  be  increased  to  59  inches  with 
the  minimum  sand-thickness.  The  apparatus  for  regulating  the  rate 
of  filtration  was  described  page  52.  The  cost  of  the  entire  plant, 
including  34  acres  effective  filter-surface,  40  acres  of  sedimentation- 


APPENDIX    VIII. 


271 


basins,  over  2  miles  of  8i-foot  conduit,  pumping-machinery,  sand- 
washing  apparatus,  laboratory,  etc.,  was  about  9,500,000  marks,  or 
$2,280,000.  This  all  reckoned  on  the  effective  filter  area  is  $67,000 
per  acre,  or  $3.80  per  head  for  a  population  of  600,000. 

The  death-rate  since  the  introduction  of  filtered  water  has  been 
lower  than  ever  before  in  the  history  of  the  city,  but  as  it  is  thought 
that  other  conditions  may  help  to  this  result,  no  conclusions  are  as 
yet  drawn. 


DEATHS    IN    HAMBURG    FROM    ALL    CAUSES,   AND    FROM    TYPHOID 
FEVER,  BEFORE  AND   AFTER   THE  INTRODUCTION   OF   FILTERS. 


Year. 


Deaths  from 

Deaths  from      Typhoid 
Fever  per 

IOO,( 


all  Causes 
per  looo 
Living. 


Living. 


1880 24.9 

1881 24.1 

1882 23.7 

1883 25.2 

1884 25.1 

1885 25.3 

1886 29.0 

1887 26.6 

1888 24.5 

1889 23.5 

1890 22.0 

1891 23-4 

1892 4I.I 

1893 20.2 

1894 17-9 

1895 19.0 

1896 17-3 

1897 I7.O 

1898 17.5 

Average  for  5  years,  exclud- 
ing  cholera    year,   before 

filtration,  1887  to  1891 24.0 

Average  for  5  years  with  fil- 
tration, 1894  to  1898 17.7 


26 
30 
27 
25 
26 
42 
7i 
88 
54 
43 
27 
24 

34 
18 

7 
II 

6 

7 
5 


47.2 
7.2 


Cholera  year. 

Filtered  water  from  May  28. 


272  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


APPENDIX  IX. 
NOTES  ON  SOME  OTHER  EUROPEAN  WATER-SUPPLIES. 

Amsterdam. — The  water  is  derived  from  open  canals  in  the 
dunes.  These  canals  have  an  aggregate  length  of  about  1 5  miles, 
and  drain  about  6200  acres.  The  water,  as  it  enters  the  canals 
from  the  fine  dune-sand,  contains  iron,  but  this  is  oxidized  and 
deposited  in  the  canals.  The  water  after  collection  is  filtered.  It 
has  been  suggested  that  by  using  covered  drains  instead  of  open 
canals  for  collecting  the  water,  the  filtration  would  be  unnecessary ; 
but,  on  the  other  hand,  the  cost  of  building  and  maintaining  cov- 
ered drains  in  the  very  fine  sand  would  be  much  greater  than 
that  of  the  canals,  and  it  is  believed,  also,  that  the  water  so  col- 
lected would  contain  iron,  the  removal  of  which  might  prove 
as  expensive  as  the  present  filtration.  In  1887  filters  were  built 
to  take  water  from  the  river  Vecht,  but  the  city  has  refused  to 
allow  the  English  company  which  owns  the  water-works  to  sell 
this  water  for  domestic  purposes,  and  it  is  only  used  for  public 
and  manufacturing  purposes,  only  a  fraction  of  the  available  sup- 
ply being  required.  Leyden,  the  Hague,  and  some  other  Dutch 
cities  have  supplies  like  the  dune  supply  of  Amsterdam,  and 
they  are  invariably  filtered. 

Antwerp  is  also  supplied  by  an  English  company.  The  raw 
water  is  drawn  from  a  small  tidal  river,  which  at  times  is  polluted 
by  the  sewage  of  Brussels.  It  is  treated  by  metallic  iron  in  Ander- 
son revolver  purifiers,  and  is  afterward  filtered  at  a  rather  low 
average  rate.  The  hygienic  results  are  closely  watched  by  the  city 
authorities,  and  are  said  to  be  satisfactory. 

Rotterdam. — The  raw  water  is  drawn  from  the  Maas,  as  the 


APPENDIX  IX,  273 

Dutch  call  the  main  stream  of  the  Rhine  after  it  crosses  their 
border.  The  population  upon  the  river  and  its  tributaries  in 
Switzerland,  Germany,  Holland,  France,  and  Belgium  is  very  great ; 
but  the  flow  is  also  great,  and  the  low  water  flow  is  exception- 
ally large  in  proportion  to  the  average  flow,  on  account  of  the 
melting  snow  in  summer  in  Switzerland,  where  it  has  its  origin. 

The  original  filters  had  wooden  under-d rains,  and  there  was 
constant  trouble  with  crenothrix  until  the  filters  were  recon- 
structed without  wood,  since  which  time  there  has  been  no 
farther  trouble.  The  present  filters  are  large  and  well  managed. 
There  is  ample  preliminary  sedimentation. 

Schiedam. — The  filters  at  Schiedam  are  comparatively  small, 
but  are  of  unusual  interest  on  account  of  the  way  in  which  they 
are  operated.  The  intake  is  from  the  Maas  just  below  Rotter- 
dam. The  city  was  unable  to  raise  the  money  to  seek  a  more 
distant  source  of  supply,  and  the  engineer,  H.  P.  N.  Halbertsma, 
was  unwilling  to  recommend  a  supply  from  so  doubtful  a  source 
without  more  thorough  treatment  than  simple  sand-filtration  was 
then  thought  to  be.  The  plan  adopted  is  to  filter  the  sup- 
ply after  preliminary  sedimentation  through  two  filters  of  0.265 
acre  each,  and  the  resulting  effluent  is  then  passed  through  three 
other  filters  of  the  same  size.  River  sand  is  used  for  the  first, 
and  the  very  fine  dune  sand  for  the  second  filtration.  The  cost 
both  of  construction  and  operation  was  satisfactory  to  the  city, 
and  much  below  that  of  any  other  available  source ;  and  the 
hygienic  results  have  been  equally  satisfactory,  notwithstanding 
the  unfavorable  position  of  the  intake. 

Magdeburg. — The  supply  is  drawn  from  the  Elbe,  and  is  fil- 
tered through  vaulted  filters  after  preliminary  sedimentation.  The 
pollution  of  the  river  is  considerable,  although  less  than  at  Altona 
or  even  at  Hamburg.  The  city  has  been  troubled  at  times  by 
enormous  discharges  of  salt  solution  from  salt-works  farther  up, 
which  at  extreme  low  water  have  sometimes  rendered  the  whole 
river  brackish  and  unpleasant  to  the  taste  ;  but  arrangements  have 


2/4  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

now  been  made  which,  it  is  hoped,  will  prevent  the  recurrence  of 
this  trouble. 

Breslau  is  supplied  with  filtered  water  from  the  river  Oder, 
which  has  a  watershed  of  8200  square  miles  above  the  intake, 
and  is  polluted  by  the  sewage  from  cities  with  an  aggregate  popu- 
lation of  about  200,000,  some  of  which  are  in  Galicia,  where  cholera 
is  often  prevalent.  In  recent  years  the  city  has  been  free  from 
cholera,  and  from  more  than  a  very  limited  number  of  typhoid- 
fever  cases  ;  but  the  pollution  is  so  great  as  to  cause  some  anxi- 
ety, notwithstanding  the  favorable  record  of  the  filters,  and  there 
is  talk  of  the  desirability  of  securing  another  supply.  Until 
1893  there  were  four  filter-beds,  with  areas  of  1.03  acres  each, 
and  not  covered.  In  1893  a  fifth  bed  was  added.  This  is 
covered  by  vaulting  and  is  divided  into  four  sections,  which  are 
separately  operated,  so  that  it  is  really  four  beds  of  0.25  acre  each. 
The  vaulting  is  concrete  arches,  supported  by  steel  I  beams  in 
one  direction. 

Budapest. — A  great  variety  of  temporary  water-supplies  have 
at  different  times  been  used  by  this  rapidly  growing  city.  The 
filters  which  for  some  years  have  supplied  a  portion  of  the  supply 
have  not  been  altogether  satisfactory  ;  but  perhaps  this  was  due 
to  lack  of  preliminary  sedimentation  for  the  extremely  turbid 
Danube  water,  and  also  to  inadequate  filter-area.  The  city  is 
rapidly  building  and  extending  works  for  a  supply  of  ground- 
water,  and  in  1894  the  filters  were  only  used  as  was  necessary  to 
supplement  this  supply,  and  it  was  hoped  that  enough  well-water 
would  be  obtained  to  allow  the  filters  to  be  abandoned  in  the  near 
future.  The  Danube  above  the  intake  receives  the  sewage  of 
Vienna  and  innumerable  smaller  cities,  but  the  volume  of  the  river 
is  very  great  compared  to  other  European  streams,  so  that  the  rela- 
lative  pollution  is  not  so  great  as  in  many  other  places. 

Zurich. — The  raw  water  is  drawn  by  the  city  from  the  Lake 
of  Zurich  near  its  outlet,  and  but  a  few  hundred  feet  from  the 
heart  of  the  city.  Although  no  public  sewers  discharge  into  the 


APPENDIX  IX.  275 

lake,  there  is  some  pollution  from  boats  and  bathers  and  other 
sources,  and,  judging  by  the  number  of  bacteria  in  the  raw  water, 
this  pollution  is  increasing.  The  raw  water  is  extremely  free 
from  sediment,  and  the  filters  only  become  clogged  very  slowly. 
The  rate  of  filtration  is  high,  habitually  reaching  7,000,000  gal- 
lons per  acre  daily ;  but,  with  the  clear  lake  water  and  long 
periods  between  scrapings,  the  results  are  excellent  even  at  this 
rate.  The  filters  are  all  covered  with  concrete  groined  arches. 

Filtration  was  commenced  in  1886,  and  was  followed  by  a 
sharp  decline  in  the  amount  of  typhoid  fever,  which,  up  to  that 
time,  had  been  rather  increasing;  for  the  six  years  before  the 
change  there  were  sixty-nine  deaths  from  this  cause  annually  per 
100,000  living,  and  for  the  six  years  after  only  ten,  or  one  seventh 
as  many ;  and  this  reduction  is  attributed  by  the  local  authori- 
ties to  the  filtration.* 

St.  Petersburg. — The  supply  is  drawn  from  the  Neva  River  by 
an  English  company,  and  is  filtered  through  vaulted  filters  at  a 
very  high  rate. 

Warsaw. — The  supply  is  drawn  from  the  Weichsel  River  by 
the  city,  and  is  filtered  through  vaulted  filters  after  preliminary 
sedimentation  at  a  rate  never  exceeding  2,570,000  gallons  per 
acre  daily. 

THE  USE  OF  UNFILTERED   SURFACE-WATERS. 

The  use  of  surface-water  without  filtration  in  Europe  is  com- 
paratively limited.  In  Germany  this  use  is  now  prohibited  by  the 
Imperial  Board  of  Health.  In  Great  Britain,  Glasgow  draws  its 
supply  unfiltered  from  Loch  Katrine ;  and  Manchester  and  some 
other  towns  use  unfiltered  waters  from  lakes  or  impounding  reservoirs 
the  watersheds  of  which  are  entirely  free  from  population.  The  best 
English  practice,  however,  as  in  Germany,  requires  the  filtration  of 
such  waters  even  if  they  are  not  known  to  receive  sewage,  and  the 

*Licht-u.  Wasserwerke,  Zurich,  1892,  page  32. 


276  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

unpolluted  supplies  of  Liverpool,  Bradford,  Dublin,  and  many  other 
cities  are  filtered  before  use. 

THE   USE  OF  GROUND-WATER.* 

Ground-waters  are  extensively  used  in  Europe,  and  apparently  in 
some  localities  the  geological  formations  are  unusually  favorable  to 
this  kind  of  supply.  Paris  derives  all  the  water  it  now  uses  for  do- 
mestic purposes  from  springs,  but  has  a  supplementary  supply  from 
the  river  for  other  purposes.  Vienna  and  Munich  also  obtain  their 
entire  supplies  from  springs,  while  Budapest,  Cologne,  Leipzig,  Dres- 
den, Frankfurt,  many  of  the  great  French  cities,  Brussels,  a  part  of 
London,  and  many  other  English  cities  derive  their  supplies  from 
wells  or  filter-galleries,  and  among  the  smaller  cities  all  over  Europe 
ground-water  supplies  are  more  numerous  than  other  kinds. 

*  Descriptions  of  some  of  the  leading  European  ground-water  supplies  were  given 
by  the  author  in  the  jour.  Asso.  Eng.  Soc.,  Feb.  1895,  p.  113. 


APPENDIX  X.  277 


APPENDIX  X. 
LITERATURE  OF    FILTRATION. 

THE  following  is  a  list  of  a  number  of  articles  on  filtration.  The 
list  is  not  complete,  but  it  is  believed  that  it  contains  the  greater  part 
of  articles  upon  slow  sand-filtration,  and  that  it  will  prove  serviceable 
to  those  who  wish  to  study  the  subject  more  in  detail. 

ANKLAMM.     Glasers  Armalen,  1886,  p.  48. 

A  description  of  the  Tegel  filters  at  Berlin,  with  excellent  plans, 
BAKER.     Engineering  News. 

Water  purification  in  America:  a  series  of  descriptions  of  filters,, 
as  follows  :  Aug.  3,  1893,  Lawrence  filter  and  description  of  appara- 
tus of  screening  sand  and  gravel;  Apr.  26,  1894,  filter  at  Nantucket, 
Mass.;  June  7,  1894,  filters  at  Ilion,  N.  Y.,  plans;  June  14,  1894, 
filters  at  Hudson,  N.  Y.;  July  12,  1894,  filters  at  Zurich,  Switzerland, 
plans  ;  Aug.  23,  1894,  filters  at  Mt.  Vernon,  N.  Y.,  plans. 
BERTSCHINGER.  Journal  fur  Gas-  und  Wasserversorgung,  1889,  p.  1126. 
A  record  of  experiments  made  at  Zurich  upon  the  effect  of  rate 
cf  filtration,  scraping,  and  the  influence  of  vaulting.  Rate  and  vault- 
ing were  found  to  be  without  effect,  but  poorer  results  followed  scrap- 
ing. The  numbers  of  bacteria  in  the  lake-water  were  too  low  to 
allow  conclusive  results. 

Journal  fur  Gas-  und  Wasserversorgung,  1891,  p.  684. 

A  farther  account  of  the  Zurich  results,  with  full  analyses  and 
a  criticism  of  Frankel  and  Piefke's  experiments. 
BOLTON.     Pamphlet,  1884. 

Descriptions  and  statistics  of  London  filters. 
BOTTCHER  and  OHNESORGE.     Zeitschrift  fur  Bauwesen,  1876,  p.  343. 

A  description  of  the  Bremen  works,  with  full  plans. 
BURTON.    Water-supply  of  Towns.     London,  1894. 

Pages  94-115  are  upon  filtration  and  mention  a  novel  method 
of  regulating  the  rate. 
CODD.     Engineering  News,  Apr.  26,  1894. 

A  description  of  a  filter  at  Nantucket,  Mass. 


278  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

CRAMER.     Centralblatt  fur  Bauwesen,  1886,  p.  42. 

A  description  of  filters  built  at  Brieg,  Germany. 
CROOK.     London  Water-supply.     London,  1883. 
DELBRUCK.     Allgemeine  Bauzeitung,  1853,  p.  103. 

A  general  article  on  filtration  ;  particularly  valuable  for  notices 
of  early  attempts  at  filtration  and  of  the  use  of  alum. 
^Deutsche  Verein  von  Gas-  und  Wasserfachmanner. 

Stenographic  reports  of  the  proceedings  of  this  society  are  printed 
regularly  in   the   Journal  fiir  Gas-  und  Wasserversorgung,  and   the 
discussions  of  papers  are  often  most  interesting. 
DROWN.     Journal  Association  Eng.  Societies,  1890,  p.  356. 

Filtration  of  natural  waters. 
FISCHER.     Vierteljahresschrift  fiir  Gesundheitspflege,  1891,  p.  82. 

Discussion  of  papers  on  water-filtration. 
FRANKEL.     Vierteljahresschrift  fiir  Gesundheitspflege,  1891,  p.  38. 

On  filters  for  city  water-works. 
FRANKEL  and    PIEFKE.     Zeitschrift  fiir  Hygiene,  1891,  p.  38,  Leistungen 

der  Sandfiltern. 

E.  FRANKLAND.     Report  in  regard  to  the  London  filters  for  1893  in  the 
Annual  Summary  of  Births,  Deaths,  and  Causes  of  Death  in  London 
and   Other    Great    Towns,    1893.       Published    by    authority    of    the 
Registrar-General. 
P.  FRANKLAND.     Proc.  Royal  Society,  1885,  p.  379. 

The  removal  of  micro-organisms  from  water. 

Proceedings  Inst.  Civil  Engineers,  1886,  Ixxxv.  p.  197. 

Water-purification  ;  its  biological  and  chemical  basis. 

Trans,  of  Sanitary  Institute  of  Great  Britain,  1886. 

Filtration  of  water  for  town  supply. 
FRUHLING.     Handbuch  der  Ingenieurwissenschaften,  vol.  ii. 

Chapter  on  water-filtration  gives  general  account  of  filtration, 
with  details  of  Konigsberg  filters  built  by  the  author  and  not  else- 
where published. 

FULLER.     Report  Mass.  State  of  Board  of  Health,  1892,  p.  449. 

"      "        "       "       "         1893,  p.  453. 

Accounts  of  the  Lawrence  experiments  upon  water-filtration  for 
1892  and  1893. 

American  Public  Health  Association,  1893,  p.  152. 

On    the   removal  of  pathogenic  bacteria   from   water   by  sand 
filtration. 
—  American  Public  Health  Association,  1894,  p.  64. 

Sand  filtration  of  water  with  special  reference  to  results  obtained 
at  Lawrence,  Mass. 


APPENDIX  X.  279 

OILL.     Deutsche  Bauzeitung,  1881,  p.  567. 

On  American  rapid  filters.  The  author  shows  that  they  are  not 
to  be  thought  of  for  Berlin,  as  they  would  be  more  expensive  as  well 
as  probably  less  efficient  than  the  usual  procedure. 

Journal  fur  Gas-  und  Wasserversorgung,  1892,  p.  596. 

A  general  account  of  the  extension  of  the  Berlin  filters  at  Miig- 
gel.  No  drawings. 

GRAHN.     Journal  fur  Gas-  und  Wasserversorgung,  1877,  p.  543. 
On  the  filtration  of  river-waters. 

Journal  fiir  Gas-  und  Wasserversorgung,  1890,  p.  511. 

Filters  for  city  water-works. 

Vierteljahresschrift  fur  Gesundsheitpflege,  1891,  p.  76. 

Discussion  of  papers  presented  on  filtration. 

Journal  fur  Gas-  und  Wasserversorgung,  1894,  p.  185. 

A  history  of  the  "  Rules  for  Water-filtration  "  (Appendix  I),  with 
some  discussion  of  them. 

GRAHN  and  MEYER.     Reiseberichte  iiber  kiinstliche  central  Sandfiltra- 
tion.     Hamburg,  1876. 

An  account  of  the  observations  of  the  authors  in  numerous  cities, 
especially  in  England. 
GRENZMER.     Centralblatt  der  Bauverwaltung,  1888,  p.  148. 

A  description  of  new  filters  at  Amsterdam,  with  plans. 
GRUBER.     Centralblatt  fiir  Bacteriologie,  1893,  p.  488. 

Salient  points  in  judging  of  the  work  of  sand-filters. 
HALBERTSMA.     Journal  fiir  Gas-  und  Wasserversorgung,  1892,  p.  43. 

Filter-works  in  Holland.  Gives  sand,  gravel,  and  water  thick- 
ness, with  diagrams. 

Journal  fiir  Gas-  und  Wasserversorgung,  1892,  p.  686. 

Description  of  filters  built  by  the  author  at  Leeuwarden,  Hol- 
land, with  plans. 
HART.     Proceedings  Inst.  of  Civil  Engineers,  1890,  c.  p.  217. 

Description  of  filters  at  Shanghai. 
HAUSEN.     Journal  fiir  Gas-  und  Wasserversorgung,  1892,  p.  332. 

An   account  of  experiments  made  for  one  year  with  three  16- 
inch  filters  at  Helsingfors,  Finland,  with  weekly  analyses  of  effluents. 
HAZEN.     Report  of  Mass.  State  Board  of  Health,  1891,  p.  601. 
Experiments  upon  the  filtration  of  water. 

Report  of  Mass.  State  Board  of  Health,  1892,  p.  539. 

Physical  properties  of  sands  and  gravels  with  reference  to  their 
use  in  filtration.     (Appendix  III.) 
HUNTER.     Engineering,  1892,  vol.  53,  p.  621. 

Description  of  author's  sand-washing  apparatus. 


2 30  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

KIRKWOOD.     Filtration  of  River- waters.     New  York,  1869. 

A  report  upon  European  niters  for  the  St.  Louis  Water  Board  in 
1866.  Contains  a  full  account  of  thirteen  filtration-works  visited  by 
the  author,  and  of  a  number  of  filter-galleries,  with  a  project  for  filters 
for  St.  Louis.  This  project  was  never  executed,  but  the  report  is  a 
wonderful  work  which  appeared  a  generation  before  the  American 
public  was  able  to  appreciate  it.  It  was  translated  into  German,  and 
the  German  edition  was  widely  circulated  and  known. 
KOCH.  Zeitschrift  fur  Hygiene,  1893. 

Water-filtration    and  Cholera :    a   discussion   of  the    Hamburg 
epidemic  of  1892  in  reference  to  the  effect  of  filtration. 
KROHNKE.     Journal  fur  Gas-  und  Wasserversorgung,  1893,  p.  513. 

An  account   of  experiments   made   at   Hamburg,  as  a  result  of 
which   the  author  recommends  the  addition  of  cuprous  chloride  to 
the  water  before  filtration  to  secure  greater  bacterial  efficiency. 
KUMMEL.     Journal  fiir  Gas-  und  Wasserversorgung,  1877,  p.  452. 
Operation  of  the  Altona  filters,  with  analyses. 

Vierteljahresschrift  fiir  Gesundheitspflege,  1881,  p.  92. 

The  water-works  of  the  city  of  Altona. 

Journal  fiir  Gas-  und  Wasserversorgung,  1887,  p.  522. 

An  article  opposing  the  use  of  rapid  filters  (David's  process). 

Journal  fiir  Gas-  und  Wasserversorgung,  1890,  p.  531. 

A  criticism  of  Frankel  and  Piefke's  results,  with  some  statistics 
of  German  and  English  filters.  (The  English  results  are  taken  with- 
out credit  from  Kirkwood.) 

Vierteljahresschrift  fiir  Gesundheitspflege,  1891,  p.  87. 

Discussion  of  papers  on  filtration,  with  some  statistics. 

Vierteljahresschrift  fiir  Gesundheitspflege,  1892,  p.  385. 

The  epidemic  of  typhoid-fever  in  Altona  in  1891. 

Journal  fiir  Gas-  und  Wasserversorgung,  1893,  p.  161. 

Results  of  experiments  upon  filtration  made  at  Altona,  and 
bacterial  results  of  the  Altona  filters  in  connection  with  typhoid 
death-rates. 

Trans.  Am.  Society  of  Civil  Engineers,  1893,  xxx.  p.  330. 

Questions  of  water-filtration. 
LESLIE.     Trans.  Inst.  Civil  Engineers,  1883,  Ixxiv.  p.  no. 

A  short  description  of  filters  at  Edinburgh. 

LINDLEY.  A  report  for  the  commissioners  of  the  Paris  Exposition  of 
1889  upon  the  purification  of  river-waters,  and  published  in  French 
or  German  in  a  number  of  journals,  among  them  Journal  fur  Gas- 
und  Wasserversorgung,  1890,  p.  501. 


APPENDIX  X.  28l 

This  is  a  most  satisfactory  discussion  of  the  conditions  which 
modern  experience  has  shown  to  be  essential  to  successful  filtration. 
MASON.     Engineering  News,  Dec.  7,  1893. 

Filters  at  Stuttgart,  Germany,  with  plans. 
MEYER  and  SAMUELSON.     Deutsche  Bauzeitung,  1881,  p.  340. 

Project  for  filters    for  Hamburg,  with    diagrams.      Except  in 
detail,  this  project  is  the  same  as  that  executed  twelve  years  later. 
MEYER.     Deutsche  Bauzeitung,  1892,  p.  519. 

Description  of  the  proposed  Hamburg  filters,  with  diagrams. 
The  Water-works  of  Hamburg. 

A  paper  presented  to  the  International  Health  Congress  at 
Rome,  March  1894,  and  published  as  a  monograph.  It  contains  a 
full  description  of  the  filters  as  built,  with  drawings  and  views  in 
greater  detail  than  the  preceding  paper. 

MILLS.     Special  Report  Mass.  State  Board  of  Health  on  the  Purification 
of  Sewage  and  Water,  1890,  p.  60 1. 

An  account  of  the  Lawrence  experiments,  1888-1890. 
Report  Mass.  State  Board  of  Health,  1893,  p.  543. 

The  Filter  of  the  Water-supply  of  the  City  of  Lawrence  and  its 
Results. 
Trans.  Am.  Society  of  Civil  Engineers,  1893,  xxx.  p.  350. 

Purification  of  Sewage  and  Water  by  Filtration. 
NEVILLE.     Engineering,  1878,  xxvi.  p.  324. 

A  description  of  the  Dublin  filters,  with  plans. 
NICHOLS.     Report  Mass.  State  Board  of  Health,  1878,  p.  137. 

The  filtration  of  potable  water. 
OESTER.     Gesundheits-Ingenieur,  1893,  p.  505. 

What  is  the  Rate  of  Filtration  ?     A  purely  theoretical  discussion. 
ORANGE.     Trans.  Inst.  Civil  Engineers,  1890,  c.  p.  268. 

Filters  at  Hong  Kong. 
PFEFFER.     Deutsche  Bauzeitung,  1880,  p.  399. 

A  description  of  filters  at  Liegnitz,  Germany. 
PIEFKE.      Results   of    Natural   and   Artificial    Filtration.      Berlin,   1881. 

Pamphlet. 
Journal  fiir  Gas-  und  Wasserversorgung,  1887,  p.  595.     Die  Prin- 

cipien  der  Reinwassergewinnung  vermittelst  Filtration. 

A  sketch  of  the  theory  and  practical  application  of  filtration. 
Zeitschrift  fiir  Hygiene,  1889,  p.  128.     Aphorismen  iiber  Wasser- 
versorgung. 

A  discussion  of  the  theory  of  filtration,  with  a  number  of  ex- 
periments on  the  thickness  of  sand-layers,  etc. 


282  FILTRATION  OF  PUBLIC  WATER-SUPPLIES. 

PIEFKE.     Vierteljahresschrift  fur  Gesundheitspflege,  1891,  p.  59. 

On  filters  for  city  water-works. 
FRANKEL  and  PIEFKE.     Zeitschrift  fur  Hygiene,  1891,  p.  38. 

Leistungen  der  Sandfiltern.  An  account  of  the  partial  obstruc- 
tion of  the  Stralau  filters  by  ice,  and  a  typhoid  epidemic  which 
followed.  Experiments  were  then  made  upon  the  passage  of  cholera 
and  typhoid  germs  through  small  filters. 

PIEFKE.     Journal  fur  Gas-   und  Wasserversorgung,  1891,  p.  208.     Neue 
Ermittelungen  liber  Sandfiltration. 

The  above  mentioned  experiments  being  objected  to  on  certain 
grounds,  they  were  repeated  by  Piefke  alone,  confirming  the  previous 
observations  on  the  passage  of  bacteria  through  filters,  but  under 
other  conditions. 

Zeitschrift  fur  Hygiene,  1894,  p.  151.     Uber  Betriebsfiihrung  von 

Sandfiltern. 

A  full  account  of  the  operation  of  the  Stralau  filters  in  1893, 
with  discussion  of  the  efficiency  of  filtration,  etc. 
PLAGGE  AND  PROSKAUER.     Zeitschrift  fur  Hygiene,  n.  p.  403. 

Examination  of  water  before  and  after  filtration  at  Berlin,  with 
theory  of  filtration. 

REINCKE.     Bericht  uber  die  Medicinische  Statistik  des  Hamburgischen 
Staates  fur  1892. 

Contains  a  most  valuable  discussion  of  the  relations  of  filtration 
to  cholera,  typhoid  fever,  and  diarrhoea,  with  numerous  tables  and 
charts.     (Abstract  in  Appendix  II.) 
REINSCH.     Centralblatt  fur  Bakteriologie,  1895,  p.  881. 

An  account  of  the  operation  of  the  Altona  filters.  High  num- 
bers of  bacteria  in  the  effluents  have  often  resulted  from  the  discharge 
of  sludge  from  the  sedimentation-basins  onto  the  filters,  due  to  the 
interference  of  ice  on  the  action  of  the  floating  outlet  for  the  basins, 
and  this,  rather  than  the  direct  effect  of  cold,  is  believed  to  be  the 
direct  cause  of  the  low  winter  efficiency.  The  author  urges  the 
necessity  of  a  deeper  sand-layers  in  no  case  less  than  18  inches  thick. 
RENK.  Gesundheits-Ingenieur,  1886,  p.  54. 

Uber  die  Ziele  der  kiinstliche  Wasserfiltration. 

RUHLMANN.     Wochenblatt  fur  Baukunde,  1887,  p.  409. 

A  description  of  filters  at  Zurich. 
SALBACH.     Glaser's  Annalen,  1882. 

Filters  at  Groningen,  Holland,  built  in  1880.     Alum  used. 
SAMUELSON.     Translation  of   Kirkwood's  "  Filtration   of    River-waters " 
into  German,  with  additional  notes  especially  on  the  theory  of  filtra- 
tion and  the  sand  to  be  employed.     Hamburg,  1876. 


APPENDIX  X.  283 


SAMUELSON.     Filtration  and   constant  water-supply.     Pamphlet.     Ham- 

burg, 1882. 
-  Journal  f.  Gas-  und  Wasserversorgung,  1892,  p.  660. 

A  discussion  of  the  best  materials  and  arrangement  for  sand-filters. 
SCHMETZEN.     Deutsche  Bauzeitung,  1878,  p.  314. 

Notice   and  extended    criticism   of   Samuelson's  translation  of 
Kirkwood. 
SEDDEN.     Jour.  Asso.  Eng.  Soc.,  1889,  p.  477. 

In  regard  to  the  sedimentation  of  river-waters. 
SEDGWICK.     New  England  Water-works  Association,  1892,  p.  103. 

European  methods  of  Filtration  with   Reference  to  American 
Needs. 
SOKAL.     Wochenschrift  der  ostreichen  Ingenieur-Verein,  1890,  p.  386. 

A  short  description  of  the  niters  at  St.  Petersburg,  and  a  com- 
parison with  those  at  Warsaw. 
STURMHOFEL.     Zeitschrift  f.  Bauwesen,  1880,  p.  34. 

A  description  of  the  Magdeburg  niters,  with  plans. 
TOMLINSON.     American  Water-  works  Association,  1888. 

A  paper  on  niters  at  Bombay  and  elsewhere. 
TURNER.     Proc.  Inst.  Civil  Engineers,  1890,  c.  p.  285. 

Filters  at  Yokohama. 
VAN    DER  TAK.     Tijdschrift   van   de    Maatschapping  van  Bouwkunde. 


A  description  (in  Dutch)  of  the  Rotterdam  water-works,  includ- 
ing the  wooden  drains  which  caused  the  trouble  with  crenothrix, 
and  which  have  since  been  removed.  Diagrams. 

VAN  IJSSELSTEYN.     Tijdschrift  van  het  Koninklijk  Instituut  van  Ingen- 
ieurs,  1892-5,  p.  173. 

A  description  of  the  new  Rotterdam  filters,  with  full  drawings. 
VEITMEYER.     Verhandlungen  d.  polyt.  Gesell.  zu  Berlin,  April,  1880. 

Filtration  and  purification  of  water. 

WOLFFHUGEL.     Arbeiten  aus  dem  Kaiserliche  Gesundheitsamt,  1886,  p.  i. 
Examinations  of  Berlin  water  for  1884-5,  witn  remarks  showing 
superior  bacterial  efficiency  with  open  filters. 
-  Journal  fur  Gas-  u.  Wasserversorgung,  1890,  p.  516. 

On  the  bacterial  efficiency  of  the  Berlin  filters,  with  diagrams. 
ZOBEL.     Zeitschrift  des  Vereins  deutsche  Ingenieure,  1884,  p.  537. 
Description  of  filters  at  Stuttgart. 


284  FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


OTHER  LITERATURE. 

Many  scientific  and  engineering  journals  publish  from  time  to 
time  short  articles  or  notices  on  filtration  which  are  not  included  in 
the  above  list.  Among  such  journals  none  gives  more  attention  to 
filtration  than  the  Journal  fur  Gasbeleuchtung  und  Wasserversorgung^ 
which  publishes  regularly  reports  upon  the  operation  of  many  Ger- 
man filters,  and  gives  short  notices  of  new  construction.  The  first 
articles  upon  filtration  in  this  journal  were  a  series  of  descriptions  of 
German  water-works  in  1870-73,  including  descriptions  of  filters  at 
Altona,  Brunswick,  Liibeck,  etc.  Stenographic  reports  of  many 
scientific  meetings  have  been  published,  particularly  since  1890,  and 
since  1892  there  has  been  much  discussion  in  regard  to  the  "  Rules 
for  Filtration  "  given  in  Appendix  I. 

A  Report  of  a  Royal  Commission  to  inquire  into  the  water- 
supply  of  the  metropolis,  with  minutes  of  evidence,  appendices,  and 
maps  (London,  1893-4),  contains  much  valuable  material  in  regard 
to  filtration. 

The  monthly  reports  of  the  water  examiner,  and  other  papers 
published  by  the  Local  Government  Board,  London,  are  often  of 
interest. 

The  German  "Verein  von  Gas-  u.  Wasserfachmanner "  prints 
without  publishing  a  most  useful  annual  summary  of  German  water- 
works statistics  for  distribution  to  members.  Many  of  the  statistics 
given  in  this  volume  are  from  this  source. 

Description  of  the  filters  at  Worms  was  given  in  the  Deutsche 
Bauzeitung,  1892,  p.  508  ;  of  the  filters  at  Liverpool  in  Engineering, 
1889,  p.  152,  and  1892,  p.  739.  The  latter  journal  also  has  given  a 
number  of  descriptions  of  filters  built  in  various  parts  of  the  world 
by  English  engineers,  but,  excepting  the  articles  mentioned  in  the 
«bove  list,  the  descriptions  are  not  given  in  detail. 


APPENDIX  X.  285 

MORE    RECENT   ARTICLES. 

THE  following  are  a  few  of  the  more  important  articles  which 
have  appeared  since  the  first  edition  of  this  book.  In  addition  many 
articles  of  current  interest  have  appeared  in  the  technical  journals, 
particularly  in  the  journals  mentioned  above. 

CLARK.     Reports  of  Mass.  State  Board  of  Health,  189410  1897,  inclusive. 
Articles  on  the  filtration  of  water,  giving  accounts  of  experiments 
at  the  Lawrence  Experiment  Station,  and  records  of  the  operation 
of  the  Lawrence  city  filter.     These  experiments  are  directed  prin- 
cipally to  the  removal  of  bacteria  from  sewage-polluted  waters. 

Jour.  New  England  Water  Works  Assoc.,  XI.,  p.  277. 

Removal  of  Iron  from  Ground  Waters.    A  description  of  certain 
experiments. 
FOWLER.     Jour.  New  England  Water  Works  Assoc.,  XII.,  p.  209. 

The  Operation  of    a   Slow   Sand  Filter.     A  most    helpful   and 
thorough  description  of  the  operation  of  sand  filters  at  Poughkeepsie 
for  a  long  period  of  years. 
FULLER.     Water  Purification  at  Louisville.    D.  Van  Nostrand  Co.,  1898. 

A  report  upon  a  series  of  most  exhaustive  experiments  carried 
out  at  Louisville,  directed  principally  to  the  clarification  of  exces- 
sively muddy  waters.  Contains  a  full  account  of  methods  of  coagula- 
tion, and  of  experiments  with  the  electrical  treatment  of  water. 

Report  on  Water  Filtration  at  Cincinnati.     City  document,  1899. 

Account  of  experiments  with  sand  filters,  with  and  without 
coagulants,  and  with  other  processes  applied  to  the  Ohio  River  water 
at  Cincinnati. 

GILL.     Filters  at  Muggel.     Proc.   Institute  of  Civil  Engineers,   1894-5; 
vol.  119,  p.  236. 

A  description  of  the  new  vaulted  filter  plant  designed  by  the 
author  for  Berlin,  Germany.  Plans  and  views. 

GOETZE.     Journal  fur  Gasbeleuchtung  und  Wasserversorgung,  1897,  p. 
169. 

Selbstthatige  Wasseraustrittsregler  besonders  fur  Filter.  A  de- 
scription of  the  automatic  regulating  device  for  filters  used  at  Bremen. 

Zeitschrift  des  Vereines  deutscher  Ingenieure,  XXX. 

Reinigung  des  Trinkwassers  in  Bremen  durch  mehrmalige  Sand- 
filtration.  A  description  of  the  method  of  double  filtration  used  at 
Bremen,  giving  results  obtained  in  full.  No  drawings. 


286  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

GRAHN.     Journal  fiir  Gasbeleuchtung  und  Wasserversorgung,  1895. 

Water  purification  plant  at  the  city  of  Magdeburg.  A  descrip- 
tion of  the  old  plant,  and  the  changes  which  have  been  made  in  it  to 
increase  its  capacity,  and  make  it  conform  to  the  requirements  of  the 
German  official  instructions  regarding  filtration.  Many  illustrations 
and  plans. 

HALBERTSMA.     Journal  ftir  Gasbeleuchtung  und  Wasserversorgung,  1896. 
Die  Resultate  der  doppelten  Filtration  zu  Schiedam.    A  descrip- 
tion of  double  filtration  at  Schiedam,  with  the  bacterial  results  for 
the  two  years,  1894  and  1895,  showing  an  average  bacterial  efficiency 
of  99.76  per  cent. 

HAZEN.  Report  to  Filtration  Commission,  Pittsburgh.  City  document, 
1899. 

A  description  of  experiments  upon  the  treatment  of  the  Allegheny 
River  water  by  sand  and  mechanical  filters. 
-  Ohio  State  Board  of  Health  Report,  1897,  p.  154. 

Report  on  the  Mechanical  Filtration  of  the  Public  Water  Supply 
of  Lorain.  Gives  the  results  of  a  five-weeks  test  of  the  Jewell  mechan- 
ical filters  at  Lorain,  treating  Lake  Erie  water. 

KEMNA.  The  Biology  of  Sand  Filtration.  Read  before  the  annual  con- 
vention of  the  British  Association  of  Water  Works  Engineers.  Ab- 
stract in  Engineering  News,  XLL,  p.  419. 

Describing  organisms  which  develop  in  open  sand  filters,  both 
animal  and  vegetable,  and  their  effects  upon  the  process.  A  quite  full 
account  of  the  author's  extended  experience,  and  the  only  paper  treat- 
ing this  subject. 

MAGAR.     Journal  fiir  Gasbeleuchtung  und  Wasserversorgung,  1897,  p.  4. 
Reinigungsbetrieb  der  offener  Sandfilter  des  Hamburger  Filter- 
werkes   in  Frostzeiten.     A  new   method  of  cleaning  open   filters  in 
winter  without  the  removal  of  the  ice. 

PANWITZ.     Arbeiten  aus  dem  Kaiserlichen  Gesundheitsamte,  XIV.,  p.  153* 
Die  Filtration  von  Oberflachenwasser  in  den  deutschen  Wasser- 
werken  wahrend  der  Jahre  1894  bis  1896. 

A  description  of  the  filtration  works  in  Germany,  and  the  re- 
sults obtained  from  them,  particularly  from  the  point  of  view  of  bac- 
terial efficiency.     Results  are  graphically  shown  by  a  series  of  charts. 
REYNARD.     Le  Genie  Civil,  1896,  XXVIII. ,  p.  321. 

Purification  of  water  with  the  aid  of  metallic  iron.  Describing 
the  works  of  the  Compagnie  General  des  Eaux  for  supplying  the 
suburbs  of  Paris  with  filtered  water,  the  capacity  of  the  works 
being  over  23,000,000  gallons  daily. 


APPENDIX  X.  287 

WESTON.     Rhode  Island  State  Board  of  Health,  1894. 

Report  of  the  Results  Obtained  with  Experimental  Filters  at  the 
Pattaconset  Pumping  Station  of  the  Providence  Water  Works.  Re- 
lates particularly  to  the  bacterial  purification  obtained  with  rapid  fil- 
tration aided  by  sulphate  of  alumina.  These  were  the  first  systematic 
experiments  made  with  mechanical  filters. 

WHEELER.     Journal  of  the  New  England  Water  Works  Assoc.,  XI.,  p.  301. 
Covered  Sand  Filter  at  Ashland,  Wis. 

A  description  of  the  covered  filters  built  by  the  author  at  Ashland 
Wis.  for  the  purification  of  the  bay  water.  Views  and  drawings. 


APPENDIX    XI. 

THE  ALBANY   WATER-FILTRATION  PLANT. 
(Abridged  from  Proceedings  American  Society  of  Civil  Engineers,  Nov.  1899.) 

ALBANY,  N.  Y.,  was  originally  supplied  with  water  by  gravity 
from  certain  reservoirs  on  small  streams  west  and  north  of  the 
city.  In  time,  with  increasing  consumption,  the  supply  obtained 
from  these  sources  became  inadequate,  and  an  additional  supply 
from  the  Hudson  River  was  introduced.  The  water  was  obtained 
from  the  river  through  a  tunnel  under  the  Erie  Basin,  and  a 
pumping-station  was  erected  in  Quackenbush  Street  to  pump  it  to 
reservoirs,  one  of  which  served  also  as  the  distributing  point  for 
one  of  the  gravity  supplies.  The  intake,  which  was  used  first  in 
1873,  drew  water  from  the  river  opposite  the  heart  of  the  city, 
In  recent  years,  the  amount  of  water  drawn  from  this  source  has 
greatly  exceeded  that  obtained  from  the  gravity  sources. 

The  Hudson  River,  at  the  point  of  intake,  has  a  drainage  area 
of  8240  square  miles.  Of  this,  4541  square  miles  are  tributary  to 
the  Hudson  above  Troy,  3493  are  tributary  to  the  Mohawk,  and 
1 68  are  tributary  to  the  Hudson  below  the  Mohawk. 

The  minimum  flow  may  be  estimated  at  1657  cubic  feet  per 
second,  or  1,060,000,000  gallons  per  24  hours,  or  at  least  fifty 
times  the  maximum  consumption. 

The  cities  and  larger  towns  upon  the  river  above  the  intake, 
with  estimated  populations  and  distances,  are  as  follows: 

288 


APPENDIX  XL 


MOST    IMPORTANT   CITIES,    TOWNS,    AND    VILLAGES    ON    THE 
WATERSHED   OF    THE   HUDSON    ABOVE   ALBANY. 


Place. 

County. 

Approximate 
Distance 
above  In- 
take, Miles 

Population  in 

1880. 

1890. 

1900. 
(Estimated.) 

Rensselaer  
Albany  .          .  • 

4 
4 

5 

8 
8 

9 

28 

44 
44 
49 
51 
56 
53 
68 

75 
82 
107 
127 

56.747 
8.820 
4  r6o 
19,416 
7,432 
(1,822) 
13,655 
4,530 
9,466 
4,900 
8  421 
5.013 
7,133 
10,191 

5,591 
6,910 

33,914 
12.194 

52,523 

60,956 
12,967 

4,463 
22,509 
10,550 
1,822 
19,002 
7,014 
17,336 
9.509 
11,975 
7,768 
13,864 
16,074 
9,213 
8,783 
44,007 
14,991 
61,869 

65.470 
19.040 
4,788 
26,450 
14,980 
(1,822) 
26,450 
10,860 
3L730 
18,450 
I7,OIO 
12,040 
26,930 
25,340 
I5,l8l 
11,160 
57,090 
18,430 
76,194 

Rensselaer..  .  . 

Rensselaer..  . 
Saratoga      .  . 

Water  ford 

Schenectady  

Schenectady.  . 
Rensselaer..  .  . 
Montgomery. 
Warren.  ...'.. 

Hoosic  Falls  

Amsterdam  
Glens  Falls     

Saratoga  Springs  .... 

Saratoga  
Fulton  

Fulton 

North  Adams,  Mass.. 
Adams,  Mass  
Little  Falls           

Berkshire 
Berkshire 
Herkimer  
Oneida  

Utica       

Oneida  

Total,  not  including  rural  population  

272,838 
33 

354,672 
43 

479,415 
59 

Without  entering  into  a  detailed  discussion,  it  may  be  said 
that  the  amount  of  sewage,  with  reference  to  the  size  of  the  river 
and  the  volume  of  flow,  is  a  fraction  less  than  that  at  Lawrence, 
Mass.,  where  a  filter-plant  has  also  been  constructed,  but  the  pollu- 
tion is  much  greater  than  that  of  most  American  rivers  from  which 
municipal  water-supplies  are  taken. 

The  filtration-plant  completed  in  1899  takes  the  water  from  a 
point  about  two  miles  above  the  old  intake.  Pumps  lift  the  water 
to  the  sedimentation-basin,  from  which  it  flows  to  the  filters  and 
thence  through  a  conduit  to  the  pumping-station  previously  used. 

DESCRIPTION   OF   PLANT. 

Intake.  —  The  intake  consists  of  a  simple  concrete  structure 
in  the  form  of  a  box,  having  an  open  top  covered  with  rails  6 
inches  apart,  and  connected  below,  through  a  36-inch  pipe,  with 


290 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


'<  HUDSON  RIVER 

NEAR  INTAKE 

....     .         SCALE  Or  MILES 


FIG.  i. 


SEDIMENTATION-BASIN,  PUMPING-STATION,  AND  OUTLETS. 


SEDIMENTATION-BASIN,  AN  OUTLET,  ANU 


LABORATORY. 

[  To  face  page  290.] 


APPENDIX  XI.  29! 

a  well  in  the  pumping-station.  Before  going  to  the  pumps  the 
water  passes  through  a  screen  with  bars  2  inches  apart,  so 
arranged  as  to  be  raked  readily.  The  rails  over  the  intake  and 
this  screen  are  intended  to  stop  matters  which  might  obstruct  the 
passageways  of  the  pumps,  but  no  attempt  is  made  to  stop 
fish,  leaves,  or  other  floating  matters  which  may  be  in  the  water. 
The  arrangement,  in  this  respect,  is  like  that  of  the  filter  at 
Lawrence,  Mass.,  where  the  raw  water  is  not  subjected  to  close 
screening.  There  is  room,  however,  to  place  finer  screens  in  the 
pump-well,  should  they  be  found  desirable. 

Pumping-station.  — The  centrifugal  pumps  have  a  guaranteed 
capacity  of  16,000,000  gallons  per  24  hours  against  a  lift  of  18 
feet,  or  12,000,000  gallons  per  24  hours  against  a  lift  of  24  feet. 
The  ordinary  pumping  at  low  water  is  against  the  higher  lift,  and 
under  these  conditions  either  pump  can  supply  the  ordinary  con- 
sumption, the  other  pump  being  held  in  reserve. 

The  pumping-station  building,  to  a  point  above  the  highest 
flood-level,  is  of  massive  concrete  construction,  without  openings. 
Nearly  all  the  machinery  is  necessarily  below  this  level,  and  in 
high  water  the  sluice-gates  are  closed,  and  the  machinery  is  thus 
protected  from  flooding.  The  superstructure  is  of  pressed  brick, 
with  granite  trimmings. 

Meter  for  Raw  Water. — Upon  leaving  the  pumping-station 
the  water  passes  through  a  36-inch  Venturi  meter  having  a  throat 
diameter  of  17  inches,  the  throat  area  being  two  ninths  of  the 
area  of  the  pipe.  The  meter  records  the  quantity  of  water 
pumped,  and  is  also  arranged  to  show  on  gauges  in  the  pumping- 
station  the  rate  of  pumping. 

Aeration. — After  leaving  the  meter,  the  water  passes  to  the 
sedimentation-basin  through  eleven  outlets.  These  outlets  consist 
of  12-inch  pipes  on  end,  the  tops  of  which  are  4  feet  above 
the  nominal  flow-line  of  the  sedimentation-basin.  Each  of  these 
outlet-pipes  is  pierced  with  296  f-inch  holes  extending  from  0.5 
to  3.5  feet  below  the  top  of  the  pipe.  These  holes  are  computed 


FILTRATION  OF  PUBLIC   WATER-SUPPLIES. 


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APPENDIX  XL  293 

so  that  when  1 1,000,000  gallons  of  water  per  day  are  pumped  all 
the  water  will  pass  through  the  holes,  the  water  in  the  pipes 
standing  flush  with  the  tops.  The  water  is  thus  thrown  out  in 
3256  small  streams,  and  becomes  aerated.  When  more  than  the 
above  amount  is  pumped,  the  excess  flows  over  the  tops  of  the 
outlet-pipes  in  thin  sheets,  which  are  broken  by  the  jets. 

Regarding  the  necessity  for  aeration,  no  observations  have 
been  taken  upon  the  Hudson  River,  but,  judging  from  experience 
with  the  Merrimac  at  Lawrence,  where  the  conditions  are  in 
many  respects  similar,  the  water  is  at  all  times  more  or  less 
aerated,  and,  for  the  greater  part  of  the  year,  it  is  nearly  saturated 
with  oxygen,  and  aeration  is  not  necessary.  During  low  water  in 
summer,  however,  there  is  much  less  oxygen  in  the  water,  and  at 
these  times  aeration  is  a  distinct  advantage.  Further,  the  river- 
water  will  often  have  a  slight  odor,  and  aeration  will  tend  to 
remove  it.  The  outlets  are  arranged  so  that  they  can  be  removed 
readily  in  winter  if  they  are  not  found  necessary  at  that  season. 

Sedimentation-basin. — The  sedimentation-basin  has  an  area 
of  5  acres  and  is  9  feet  deep.  To  the  overflow  it  has  a  capacity 
of  14,600,000  gallons,  and  to  the  flow-line  of  the  filters  8,900,000 
gallons.  There  is  thus  a  reserve  capacity  of  5,700,000  gallons 
between  these  limits,  and  this  amount  can  be  drawn  upon,  without 
inconvenience,  for  maintaining  the  filters  in  service  while  the 
pumps  are  shut  down.  This  allows  a  freedom  in  the  operation  of 
the  pumps  which  would  not  exist  with  the  water  supplied  direct 
to  the  filters. 

The  water  enters  the  sedimentation-basin  from  eleven  inlets 
along  one  side,  and  is  withdrawn  from  eleven  outlets  directly 
opposite.  The  inlets  and  aerating  devices  described  previously 
bring  the  water  into  the  basin  without  current  and  evenly  dis- 
tributed along  one  side.  Both  inlets  and  outlets  are  controlled 
by  gates,  so  that  any  irregularities  in  distribution  can  be  avoided. 
The  concrete  floor  of  the  sedimentation-basin  is  built  with  even 
slopes  from  the  toe  of  each  embankment  to  a  sump,  the  heights  of 


294 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


OUTSIDE  WALL,  READY  FOR  CONCRETE  BACKING. 


SEDIMENTATION-BASIN  :  SHOWING  CONSTRUCTION  OF  FLOOR. 

{To  face  page  294.] 


APPENDIX  XI.  295 

these  slopes  being  I  foot,  whatever  their  lengths.  The  sump  is 
connected  with  a  24-inch  pipe  leading  to  a  large  manhole  in  which 
there  is  a  gate  through  which  water  can  be  drawn  to  empty  the 
basin.  There  is  an  overflow  from  the  basin  to  this  manhole  which 
makes  it  impossible  to  fill  the  basin  above  the  intended  level. 

Filters. — The  filters  are  of  masonry,  and  are  covered  to 
protect  them  against  the  winters,  which  are  quite  severe  in 
Albany.  The  piers,  cross-walls,  and  linings  of  the  outside  walls, 
entrances,  etc.,  are  of  vitrified  brick.  All  other  masonry  is  con- 
crete. The  average  depth  of  excavation  for  the  filters  was  4  feet, 
and  the  material  at  the  bottom  was  usually  blue  or  yellow  clay. 
In  some  places  shale  was  encountered.  In  one  place  soft  clay 
was  found,  and  there  the  foundations  were  made  deeper.  The 
floors  consisted  of  inverted,  groined,  concrete  arches,  arranged  to 
distribute  the  weight  of  the  walls,  and  vaulting  over  the  whole  area 
of  the  bottom. 

The  groind  arch-vaulting  is  of  concrete  with  a  clear  span  of 
1 1  feet  1 1  inches,  a  rise  of  2\  feet,  and  a  thickness  of  6  inches  at 
the  crown.  It  was  put  in  in  squares,  the  joints  being  on  the 
crowns  of  the  arches  parallel  with  the  lines  of  the  piers,  and  each 
pier  being  the  centre  of  one  square.  The  manholes  are  in  alter- 
nate sections,  and  are  of  concrete,  built  in  steel  forms  with  cast- 
ings at  the  tops,  securely  jointed  to  the  concrete. 

Above  the  vaulting  there  are  2  feet  of  earth  and  soil,  grassed 
on  top.  The  tops  of  the  manholes  are  6  inches  above  the  soil  to 
prevent  rain-water  from  entering  them.  The  drainage  of  the  soil 
is  effected  by  a  depression  of  the  vaulting  over  each  pier,  parti- 
ally filled  with  gravel  and  sand,  from  which  water  is  removed  by 
a  2-inch  tile-drain  going  down  the  centre  of  the  pier  and  discharg- 
ing through  its  side  just  above  the  top  of  the  sand  in  the  filter. 

In  order  to  provide  ready  access  to  each  filter,  a  part  of  the 
vaulting  near  one  side  is  elevated  and  made  cylindrical  in  shape, 
making  an  inclined  runway  from  the  sand-level  to  a  door  the 
threshold  of  which  is  6  inches  above  the  level  of  the  overflow. 


296 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


APPENDIX  XI. 


297 


This  sand-run   is  provided  with  permanent  timber   runways  and 
with  secure  doors. 

The  manholes  of  the  filters  are  provided  with  double  covers  of 
steel  plates  to  exclude  the  cold.      The  covers  also  exclude  light. 


I   El.  121.0 


Elevation. 
FIG.  5. — ENTRANCE  TO  A  FILTER. 

When  cleaning  the  filters,  light  can  be  admitted  by  removing  the 
covers.  Supports  for  electric  lights  are  placed  in  the  vaulting,  so 
that  the  filters  can  be  lighted  by  electricity  and  the  work  of 
cleaning  can  be  done  at  night,  and  in  winter  under  heavy  snow, 
without  removing  the  covers.  The  electric  lights  have  not  yet 
been  installed. 

The  regulator-houses,  the  entrances  to  the  sand-runs,  and  all 
exposed  work  are  of  pressed  brick  with  Milford  granite  trimmings 
and  slate  roofs.  The  regulator-houses  have  double  walls  and 
double  windows  and  a  tight  ceiling  in  the  roof,  to  make  them  as 
warm  as  possible  and  to  avoid  the  necessity  of  artificial  heat  to 
prevent  freezing. 

The  main   underdrains  for   removing  the   filtered  water  are  of 


298  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

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[  To  face  page  298.  ] 


APPENDIX   AY.  299 

vitrified  pipe  surrounded  by  concrete  and  are  entirely  below  the 
floors  of  the  filters. 

Connections  with  the  main  drain  are  made  through  thirty-eight 
6-inch  outlets  in  each  filter,  passing  through  the  floor  and  connected 
with  6-inch  lateral  drains  running  through  the  whole  width  of  the 
filter.  These  drains  were  made  with  pipes  having  one  side  of  the 
bell  cut  off  so  that  they  would  lie  flat  on  the  floor  and  make  con- 
centric joints,  without  support  and  without  having  to  be  wedged. 
They  were  laid  with  a  space  of  about  I  inch  between  the  barrels, 
leaving  a  large  opening  for  the  admission  of  water  from  the  gravel. 

The  underdrainage  system  is  so  designed  that,  when  starting 
a  filter  after  cleaning,  the  friction  of  the  sand  is  about  50  mm.  at 
a  rate  of  3,000,000  gallons  per  acre  daily,  and  the  friction  of  the 
underdrainage  system  is  estimated  at  10  mm.  This  very  low 
friction,  which  is  necessary,  is  obtained  by  the  use  of  ample  sizes 
for  the  underdrains  and  low  velocities  in  them.  In  the  outlet  and 
measuring  devices  moderate  losses  of  head  are  not  objectionable, 
and  the  sizes  of  the  pipes  and  connections  are,  therefore,  smaller 
than  the  main  underdrains. 

The  gravel  surrounding  the  underdrains  is  of  three  grades.  The 
material  was  obtained  from  the  river-bed  by  dredging,  and  was  of 
the  same  stock  as  that  used  for  preparing  ballast  for  the  concrete. 
It  was  separated  and  cleaned  by  a  special,  cylindrical,  revolving 
screen.  The  coarsest  grade  of  gravel  was  that  which  would  not 
pass  round  holes  I  inch  in  diameter,  and  free  from  stones  more 
than  about  2  inches  in  diameter.  At  first  it  was  required  to  pass 
a  screen  with  holes  2  inches  in  diameter,  but  this  screen  removed 
many  stones  which  it  was  desired  to  retain,  and  the  screen  was 
afterward  changed  to  have  holes  3  inches  in  diameter.  The  inter- 
mediate grades  of  gravel  passed  the  i-inch  holes,  and  were  retained 
by  a  screen  with  round  holes  f  inch  in  diameter.  The  finest 
gravel  passed  the  above  screens  and  was  retained  by  a  screen  with 
round  holes  T3T  inch  in  diameter.  The  gravel  was  washed,  untiJ 
free  from  sand  and  dirt,  by  water  played  upon  it  during  the 


300 


FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 


APPENDIX  XL  301 

process  of  screening,  and  it  was  afterward  taken  over  screens  in 
the  chutes,  where  it  was  separated  from  the  dirty  water,  and,  when 
necessary,  further  quantities  of  water  were  played  upon  it  at  these 
points. 

The  average  mechanical  analyses  of  the  three  grades  of  gravel 
are  shown  by  Fig.  8.  Their  effective  sizes  were  23,  8,  and 
3  mm.  respectively,  and  for  convenience  they  are  designated  by 
these  numbers.  The  average  uniformity  coefficient  for  each  grade 
was  about  1.8. 

The  23-mm.  gravel  entirely  surrounded  the  6-inch  pipe-drains, 
and  was  carried  slightly  above  their  tops.  In  some  cases  it  was 
used  to  cover  nearly  the  whole  of  the  floor,  but  this  was  not 
insisted  upon. 

The  8-mm.  gravel  was  obtained  in  larger  quantity  than  the 
other  sizes,  and  was  used  to  fill  all  spaces  up  to  a  plane  2\  inches 
below  the  finished  surface  of  the  gravel,  this  layer  being  about 
2  inches  thick  over  the  tops  of  the  drains,  and  somewhat  thicker 
elsewhere. 

The  3-mm.  gravel  was  then  applied  in  a  layer  2j  inches  deep, 
and  the  surface  levelled. 

The  preliminary  estimates  of  cost  were  based  upon  the  use  of 
filter-sand  from  a  bank  near  the  filter-site.  Further  examination 
showed  that  this  sand  contained  a  considerable  quantity  of  lime, 
and  it  was  found  by  experiment  with  a  small  filter  constructed  for 
that  purpose  that  the  use  of  this  sand  would  harden  the  water  by 
about  2  parts  in  100,000,  and  the  amount  of  lime  contained  in 
the  sand,  namely,  about  7  per  cent,  was  sufficient  to  continue  this 
hardening  action  for  a  considerable  number  of  years.  This  was 
regarded  as  a  serious  objection  to  its  use,  and  the  specifications 
were  drawn  limiting  the  amount  of  lime  in  the  sand.  This 
excluded  all  of  the  local  bank  sands.  The  river-sands  which  were 
used  were  nearly  free  from  lime,  and  in  the  end  the  sand  as 
secured  was  probably  not  only  free  from  lime,  but  more  satisfac- 


302 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 


tory  in  other  ways,  and  also  cheaper  than  the  bank-sand  would 
have  been. 

The  specifications  of  the  filter-sand  require  that  "  The  filter- 
sand  shall  be  clean  river-,  beach-,  or  bank-sand,  with  either  sharp 
or  rounded  grains.  It  shall  be  entirely  free  from  clay,  dust,  or 
organic  impurities,  and  shall,  if  necessary,  be  washed  to  remove 
such  materials  from  it.  The  grains  shall,  all  of  them,  be  of 


MECHANICAL  COMPOSITION  OF  FILTER  SAND  AND  GRAVELS* 

(ARROWS  SHOW  REQUIREMENT  OF  SPECIFICATION) 


0.4 


/i 


S/S    §    * 

*4     H     d 


#** 


7V 


0.02  0.05         0.10        0.20   0.300.400.50       1.0          2.0     3.04,05.0 

Diameters  in  Millimeters 

FIG.  8. 


30    405060 


hard  material  which  will  not  disintegrate,  and  shall  be  of  the 
following  diameters:  Not  more  than  i  per  cent,  by  weight,  less 
than  0.13  mm.,  nor  more  than  10  per  cent  less  than  0.27  mm.; 
at  least  10  per  cent,  by  weight,  shall  be  less  than  0.36  mm.,  and 
at  least  70  per  cent,  by  weight,  shall  be  less  than  I  mm.,  and  no 
particles  shall  be  more  than  5  mm.  in  diameter.  The  diameters 
of  the  sand-grains  will  be  computed  as  the  diameters  of  spheres  of 


PLACING  THE  CONCRETE  VAULTING. 


GENERAL  VIKAV  OF  VAULTING,  UNDER  CONSTRUCTION. 

[  To  face  page  302.] 


APPENDIX  XI. 


304  FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

equal  volume.  The  sand  shall  not  contain  more  than  2  per  cent, 
by  weight,  of  lime  and  magnesia  taken  together  and  calculated  as 
carbonates." 

The  sand  was  obtained  from  the  river  at  various  places  by 
dredging.  It  was  first  taken  up  by  dipper-dredges,  and  brought 
in  scows  to  a  point  in  the  back  channel  a  little  north  of  the  filter- 
plant.  It  was  there  dumped  in  a  specially  prepared  place  in  the 
bottom  of  the  river,  from  which  it  was  lifted  by  a  hydraulic  dredge 
and  pumped  through  a  15 -inch  pipe  an  average  distance  of  525 
feet  to  points  selected,  and  varied  from  time  to  time,  on  the  flats 
north  of  the  filters.  The  water  containing  the  sand  was  then  put 
through  screens  having  meshes  which  excluded  all  stones  5  mm. 
in  diameter  and  over,  and  was  then  taken  into  basins  where  the 
sand  was  deposited  and  afterward  carted  to  the  filters. 

Two  ejector  sand-washing  machines,  shown  in  Fig.  9,  are 
provided  at  convenient  places  between  the  filters.  In  them  the 
dirty  sand  is  mixed  with  water,  and  is  thrown  up  by  an  ejector, 
after  which  it  runs  through  a  chute  into  a  receptacle,  from  which 
it  is  again  lifted  by  another  ejector.  It  passes  in  all  through  five 
ejectors,  part  of  the  dirty  water  being  wasted  each  time.  The 
sand  is  finally  collected  from  the  last  ejector,  where  it  is  allowed 
to  deposit  from  the  water. 

Water  is  admitted  to  each  filter  through  a  2O-inch  pipe  from  a 
pipe  system  connecting  with  the  sedimentation-basin.  Just  inside 
of  the  filter-wall  is  placed  a  standard  gate,  and  beyond  that  a 
balanced  valve  connected  with  an  adjustable  float  to  shut  off  the 
water  when  it  reaches  the  desired  height  on  the  filter.  These 
valves  and  floats  were  constructed  from  special  designs,  and  are 
similar  in  principle  to  valves  used  for  the  same  purpose  in  the 
Berlin  water-filters. 

Each  filter  is  provided  with  an  overflow,  so  arranged  that  it 
cannot  be  closed,  which  prevents  the  water-level  from  exceeding 
a  fixed  limit  in  case  the  balanced  valve  fails  to  act.  An  outlet  is 
also  provided  near  the  sand-run,  so  that  unfiltered  water  can  be 


APPENDIX  XI.  305 

removed  quickly  from  the  surface  of  the  filter,  should  it  be  neces- 
sary, to  facilitate  cleaning. 

The  outlet  of  each  filter  is  through  a  2O-inch  gate  controlled 
by  a  standard  graduated  to  show  the  exact  distance  the  gate  is 
open.  The  water  rises  in  a  chamber  and  flows  through  an  orifice 
in  a  brass  plate  4  by  24  inches,  the  centre  of  which  is  I  foot  below 
the  level  of  the  sand-line.  At  the  nominal  rate  of  filtration, 
3,000,000  gallons  per  acre  daily,  I  foot  of  head  is  required  to  force 
the  water  through  the  orifice.  With  other  rates  the  head  increases 
or  decreases  approximately  as  the  square  of  the  rate  and  forms  a 
measure  of  it.  With  water  standing  in  the  lower  chamber,  so  that 
the  orifice  is  submerged,  it  is  assumed  that  the  same  rates  will  be 
obtained  with  a  given  difference  in  level  between  the  water  on  the 
two  sides  of  the  orifice  as  from  an  equal  head  above  the  centre  of 
the  orifice  when  discharging  into  air. 

Measurement  of  Effluent. — In  order  to  show  the  rate  of  filtra- 
tion two  floats  are  connected  with  the  water  on  the  two  sides  of 
the  orifice.  These  floats  are  counterbalanced;  one  carries  a  grad- 
uated scale,  and  the  other  a  marker  which  moves  in  front  of  the 
scale  and  shows  the  rate  of  filtration  corresponding  to  the  difference 
in  level  of  the  water  on  the  two  sides.  When  the  water  in  the 
lower  chamber  falls  below  the  centre  of  the  orifice,  the  water  in 
the  float-chamber  is  nevertheless  maintained  at  this  level.  This 
is  accomplished  by  making  the  lower  part  of  the  tube  water-tight, 
with  openings  just  at  the  desired  level,  so  that  when  the  water 
falls  below  this  point  in  the  outer  chamber  it  does  not  fall  in  the 
float-chamber. 

To  prevent  the  loss  of  water  in  the  float-chamber  by  evapora- 
tion or  from  other  causes,  a  lead  pipe  is  brought  from  the  other 
chamber  and  supplies  a  driblet  of  water  to  it  constantly;  this 
overflows  through  the  openings,  and  maintains  the  water-level  at 
precisely  the  desired  point.  The  floats  thus  indicate  the  difference 
in  water-level  on  the  two  sides  of  the  orifice  whenever  the  water 
in  the  lower  chamber  is  above  the  centre  of  the  orifice;  otherwise 


306  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

they  indicate  the  height  of  water  in  the  upper  chamber  above  the 
centre  of  the  orifice,  regardless  of  the  water-level  in  the  lower 
chamber.  The  scale  is  graduated  to  show  the  rates  of  filtration  in 
millions  of  gallons  per  acre  of  filtering  area.  In  computing  this 
scale  the  area  of  the  filters  is  taken  as  0.7  acre,  and  the  coefficient 
of  discharge  as  0.61. 

At  the  ordinary  rates  of  filtration  the  errors  introduced  by  the 
different  conditions  under  which  the  orifice  operates  will  rarely 
amount  to  as  much  as  100,000  gallons  per  acre  daily,  or  one 
thirtieth  of  the  ordinary  rate  of  filtration.  Usually  they  are  much 
less  than  this.  The  apparatus  thus  shows  directly,  and  with 
substantial  accuracy,  the  rate  of  filtration  under  all  conditions. 

Measurement  of  Loss  of  Head. — Two  other  floats  with 
similar  connections  show  the  difference  in  level  between  the  water 
standing  on  the  filter  and  the  water  in  the  main  drain-pipe  back 
of  the  gate,  or,  in  other  words,  the  frictional  resistance  of  the  filter, 
including  the  drains.  This  is  commonly  called  the  loss  of  head, 
and  increases  from  0.2  foot  or  less,  with  a  perfectly  clean  filter,  to 
4  feet  with  the  filter  ready  for  cleaning.  When  the  loss  of  head 
exceeds  4  feet  the  rate  of  filtration  cannot  be  maintained  at 
3,000,000  gallons  per  acre  daily  with  the  outlet  devices  provided, 
and,  in  order  to  maintain  the  rate,  the  filter  must  be  cleaned. 

Adjustment  of  Gauges. — The  adjustment  of  the  gauges  show- 
ing the  rate  of  filtration  and  loss  of  head  is  extremely  simple. 
When  a  filter  is  put  in  service  the  gates  from  the  lower  chamber 
to  the  pure-water  reservoir  and  to  the  drain  are  closed,  the  outlet 
of  the  filter  opened,  and  both  chambers  allowed  to  fill  to  the  level 
of  the  water  on  the  filter.  The  length  of  the  wire  carrying  the 
gauge  is  then  adjusted  so  that  the  gauge  will  make  the  desired 
run  without  hitting  at  either  end,  and  then  the  marker  is  adjusted. 
As  both  the  rate  of  filtration  and  loss  of  head  are  zero  under  these 
conditions,  it  is  only  necessary  to  set  the  markers  to  read  zero  on 
the  gauges  to  adjust  them.  The  gates  can  then  be  opened  for 
regular  operation,  and  the  readings  on  the  gauges  will  be  correct. 


INTERIOR  OF  A  FILTER  :    DRAIN,  GRAVEL  AND  SAND  LAYERS. 


INTERIOR  OF  A  FILTER,   READY  FOR  USE. 

[  To  face  page  306.] 


APPENDIX  XI. 

It  is  necessary  to  use  wires  which  are  light,  flexible,  and  whicl 
will  not  stretch.  At  first  piano-wire,  No.  27  B.  &  S.  gauge,  was 
used,  and  was  well  adapted  to  the  purpose,  except  that  it  rusted 
rapidly.  Because  of  the  rusting  it  was  found  necessary  to  substi- 
tute another  wire,  and  cold-drawn  copper  wire,  No.  24  B.  &  S. 
gauge,  was  used  with  fair  results.  Stretching  is  less  serious  than 
it  would  otherwise  be,  as  the  correctness  of  the  adjustment  can  be 
observed  and  corrected  readily  every  time  a  filter  is  out  of  service. 

From  the  lower  chambers  in  the  regulator-houses  the  water 
flows  through  gates  to  the  pipe  system  leading  to  the  pure-water 
reservoir.  Drain-pipes  are  also  provided  which  allow  the  water  to 
be  entirely  drawn  out  of  each  filter,  should  that  be  necessary  for 
any  reason,  and  without  interfering  with  the  other  filters  or  with 
the  pure-water  reservoir. 

The  outlets  of  the  filters  are  connected  in  pairs,  so  that  filtered 
water  can  be  used  for  filling  the  underdrains  and  sand  of  the  filters 
from  below  prior  to  starting,  thus  avoiding  the  disturbance  which 
results  from  bringing  dirty  water  upon  the  sand  of  a  filter  not  filled 
with  water. 

Laboratory  Building. — The  scientific  control  of  filters  is 
regarded  as  one  of  the  essentials  to  the  best  results,  and  to  provide 
for  this  there  is  a  laboratory  building  at  one  end  of  the  central 
court  between  the  filters  and  close  to  the  sedimentation-basin, 
supplied  with  the  necessary  equipment  for  full  bacterial  examina- 
tions, and  also  with  facilities  for  observing  the  colors  and  tur- 
bidities of  raw  and  filtered  waters,  and  for  making  such  chemical 
examinations  as  may  be  necessary.  This  building  also  provides  a 
comfortable  office,  dark  room,  and  storage  room  for  tools,  etc., 
used  in  the  work. 

Pure-water  Reservoir. — A  small  pure-water  reservoir,  94  feet 
square  and  holding  about  600,000  gallons,  is  provided  at  the 
filter-plant.  The  construction  is  similar  to  that  of  the  filters,  but 
the  shapes  of  the  piers  and  vaulting  were  changed  slightly,  as  there 
was  no  necessity  for  the  ledges  about  the  bottoms  of  the  piers  and 


308  FILTRATION  OF-  PUBLIC   WATER-SUPPLIES. 

walls;  while  provision  is  made  for  taking  the  rain-water,  falling 
upon  the  vaulting  above,  to  the  nearest  filters  instead  of  allowing 
it  to  enter  the  reservoir.  The  floor  and  roof  of  the  reservoir  are 
at  the  same  levels  as  those  of  the  filters. 


CAPACITY    OF   PLANT  AND    MEANS    OF   REGULATION. 

The  various  filters  have  effective  filtering  areas  of  from  0.702 
to  0.704  acre,  depending  upon  slight  differences  in  the  thickness 
of  the  walls  in  different  places.  For  the  purpose  of  computation, 
the  area  of  each  filter  is  taken  at  0.7  acre.  The  nominal  rate  of 
filtration  is  taken  as  3,000,000  gallons  per  acre  daily,  at  which 
rate  each  filter  will  yield  2,100,000  gallons  daily,  and,  with  one 
filter  out  of  use  for  the  purpose  of  being  cleaned,  seven  filters 
normally  in  use  will  yield  14,700,000  gallons.  The  entrances  and 
outlets  are  all  made  of  sufficient  size,  so  that  rates  50  per  cent 
greater  than  the  foregoing  are  possible.  The  capacities  of  the 
intake,  pumping-station,  and  piping  are  such  as  to  supply  any 
quantity  of  water  which  the  filters  can  take,  up  to  an  extreme 
maximum  of  25,000,000  gallons  in  24  hours.  The  pure-water 
conduit  from  the  filters  to  Quackenbush  Street  is  nominally  rated 
at  25,000,000  gallons  per  24  hours,  after  it  has  become  old  and 
somewhat  tuberculated.  In  its  present  excellent  condition  it  will 
carry  a  larger  quantity.. 

At  the  pumping-station  at  Quackenbush  Street  there  are  three 
Allis  pumps,  each  capable  of  pumping  5,000,000  gallons  per  24 
hours.  In  addition  to  the  above  there  are  the  old  reserve  pumps 
with  a  nominal  capacity  of  10,000,000  gallons  per  24  hours,  which 
can  be  used  if  necessary,  but  which  require  so  much  coal  that  they 
are  seldom  used.  For  practical  purposes  the  15,000,000  gallons 
represents  the  pumping  capacity  of  this  station  and  also  the 
capacity  of  the  filters,  but  the  arrangements  are  such  that  in  case 
of  emergency  the  supply  can  be  increased  to  20,000,000  or  even 
25,000,000  gallons  for  a  short  time. 


APPENDIX  XI.  309 

The  water  is  pumped  through  rising  mains  to  reservoirs  holding 
37,000,000  gallons,  not  including  the  Tivdli  low-service  reservoir, 
which  is  usually  supplied  from  gravity  sources.  The  reservoir 
capacity  is  such  that  the  pumping  can  be  suspended  at  Quacken- 
bush  Street  for  considerable  periods  if  necessary,  and  in  practice 
it  has  been  suspended  at  certain  times,  especially  on  Sundays. 
The  amount  of  water  required  is  also  somewhat  irregular.  The 
drainage  areas  supplying  the  gravity  reservoirs  are  much  larger, 
relatively,  than  the  reservoirs,  and  at  flood  periods  the  volume  of 
the  gravity  supply  is  much  greater  than  that  which  can  be  drawn 
in  dry  weather.  Thus  it  happens  that,  at  certain  seasons  of  the 
year,  the  amount  of  water  to  be  pumped  is  but  a  fraction  of  the 
nominal  capacity  of  the  pumps,  and  at  these  times  it  is  possible  to 
shut  the  pumps  down  for  greater  lengths  of  time. 

Capacity  of  Pure-water  Reservoir.  — The  storage  capacity 
provided  between  the  filters  and  the  Quackenbush  Street  pumps  is 
comparatively  small,  namely,  600,000  gallons,  or  one  hour's 
supply  at  the  full  nominal  rate.  A  larger  basin,  holding  as  much 
as  one  third  or  one  half  of  a  day's  supply,  would  be  in  many 
respects  desirable  in  this  position,  but  the  conditions  were  such  as 
to  make  it  practically  impossible.  The  bottom  of  the  reservoir 
could  not  be  put  lower  without  deepening  and  increasing  greatly 
the  expense  of  the  conduit-line.  On  the  other  hand,  the  flow-line 
of  the  reservoir  could  not  be  raised  without  raising  the  level  of  the 
filters,  which  was  hardly  possible  upon  the  site  selected.  The 
available  depth  of  the  reservoir  was  thus  limited  between  very 
narrow  bounds,  and  to  secure  a  large  capacity  would  have  necessi- 
tated a  very  large  area,  and  consequently  a  great  expense.  Under 
these  circumstances,  and  especially  in  view  of  the  abundant 
storage  capacity  for  filtered  water  in  the  distributing  reservoirs,  it 
was  not  deemed  necessary  to  provide  a  large  storage,  and  only  so 
much  was  provided  as  would  allow  the  pumps  to  be  started  at  the 
convenience  of  the  engineer,  and  give  a  reasonable  length  of  time 
for  the  filters  to  be  brought  into  operation.  For  this  the  pure- 


310  FILl^RATION   OF  PUBLIC    WATER-SUPPLIES. 

water  reservoir  is  ample,  but  it  is  not  enough  to  balance  any  con- 
tinued fluctuations  in  the  rate  of  pumping. 

Method  of  Regulating  and  Changing  the  Rate  of  Filtration. 
— With  all  the  Allis  pumps  running  at  their  nominal  capacity,  the 
quantity  of  water  required  will  just  about  equal  the  nominal 
capacity  of  the  filters.  When  only  one  or  two  pumps  are  running, 
the  rate  of  nitration  can  be  reduced.  With  the  plant  operating 
up  to  it's  full  capacity,  the  water-level  in  the  pure-water  reservoir 
will  be  below  the  level  of  the  standard  orifices  in  the  filter  outlets. 
When  the  rate  of  pumping  is  reduced,  if  no  change  is  made  in  the 
gates  controlling  the  filter  outlets,  the  water  will  gradually  rise  in 
the  pure-water  reservoir  and  in  the  various  regulator  chambers, 
and  will  submerge  the  orifices  and  gradually  reduce  the  head  on 
the  filters,  and  consequently  the  rates  of  filtration,  until  those 
rates  equal  the  quantity  pumped.  In  case  the  pumping  is  stopped 
altogether,  the  filters  will  keep  on  delivering  at  gradually  reduced 
rates  until  the  water-level  in  the  pure-water  reservoir  reaches  that 
of  the  water  on  the  filters. 

When  the  pumps  are  started  up,  after  such  stoppage  or 
reduced  rate  of  pumping,  the  water-levels  in  the  pure-water  reser- 
voir and  in  the  gate-chambers  will  be  lowered  gradually,  and  the 
filters  will  start  to  operate  it  first  with  extremely  low  rates,  which 
will  increase  gradually  until  the  water  is  depressed  below  the 
orifices,  when  they  will  again  reach  the  rates  at  which  they  were 
last  set.  The  regulators  during  all  this  time  will  show  the  rate  of 
filtration  on  each  filter,  and,  if  any  inequalities  occur  which 
demand  correction,  the  gates  on  the  various  outlets  can  be 
adjusted  accordingly. 

The  arrangement,  in  this  respect,  combines  some  of  the 
features  of  the  English  and  German  plants.  In  the  English  plants 
the  filters  are  usually  connected  directly  with  the  clear-water 
basin,  and  that  in  turn  with  the  pumps,  and  the  speed  of  filtration 
is  required  to  respond  to  the  speed  of  the  pumps,  increasing  and 
decreasing  with  it,  being  regulated  at  all  times  by  the  height  of 


CENTRAL  COURT,  SHOWING  SAND-WASHER,  DIRTY  SAND,  ETC. 


SEDIMENTATION  BASIN,  FILTERS,  ETC. 


[  To  face  page  310.] 


APPENDIX  XI.  311 

water  in  the  pure-water  reservoir.  This  arrangement  has  been 
subject  to  severe  criticism,  because  the  rate  of  filtration  fluctuates 
with  the  consumption,  and  especially  because  the  rates  of  filtration 
obtained  simultaneously  in  different  filters  may  be  different. 
There  was  no  way  to  determine  at  what  rate  any  individual  filter 
was  working,  and  there  was  always  a  tendency  for  a  freshly 
scraped  filter  to  operate  much  more  rapidly  than  those  which  had 
not  been  scraped  for  some  time. 

This  led  to  the  procedure,  first  formulated  by  the  Commission 
of  German  Water-works  Engineers  in  1894,  and  provided  for  in 
most  of  the  German  works  built  or  remodelled  since  that  time,  of 
providing  pure-water  storage  sufficient  in  amount  to  make  the  rate 
of  filtration  entirely  independent  of  the  operation  of  the  pumps. 
Each  filter  was  to  be  controlled  by  itself,  be  independent  of  the 
others,  and  deliver  its  water  into  a  pure-water  reservoir  lower  than 
itself,  so  that  it  could  n,ever  be  affected  by  back-water,  and  so 
large  that  there  would  never  be  a  demand  for  sudden  changes  in 
the  rate  of  filtration. 

This  procedure  has  given  excellent  results  in  the  German 
works;  but  it  leads  oftentimes  to  expensive  construction.  It 
involves,  in  the  first  place,  a  much  greater  loss  of  head  in  passing 
through  the  works,  because  the  pure-water  reservoir  must  be  lower 
than  the  filters,  and  the  cost  of  the  pure-water  reservoir  is 
increased  greatly  because  of  its  large  size.  The  regulation  of  the 
filters  is  put  upon  the  attendants  entirely,  or  upon  automatic 
devices,  and  regulation  by  what  is  known  as  "responding  to  the 
pumps"  is  eliminated. 

More  recently,  the  German  authorities  have  shown  less  dis- 
position to  insist  rigidly  upon  the  principles  advanced  in  1894. 
In  a  compilation  of  the  results  of  several  years'  experience  with 
German  water-filters,  Dr.  Pannwiz  *  makes  a  statement  of  partic- 
ular interest,  of  which  a  free  translation  is  as  follows: 

"  Most  of  the  German  works  have  sufficient  pure- water  reser- 
voir capacity  to  balance  the  normal  fluctuations  in  consumption, 

*"  Arbeiten  aus  dem  Kaiserlichen  Gtsundheitsamte,"  vol.  Xiv.  p.  260. 


312  FILTRATION   OF  PUBLIC    WATER-SUPPLIES. 

so  that  the  rate  of  filtration  is  at  least  independent  of  the  hourly 
fluctuations  in  consumption.  Of  especial  importance  is  the  super- 
ficial area  of  the  pure-water  reservoir.  If  it  is  sufficiently  large, 
there  is  no  objection  to  allowing  the  water-level  in  it  to  rise  to 
that  of  the  water  upon  the  filters.  With  very  low  rates  of  con- 
sumption during  the  night  the  filters  may  work  slowly  and  even 
stop,  without  damage  to  the  sediment  layers  when  the  stopping 
and  starting  take  place  slowly  and  regularly,  because  of  the  ample 
reservoir  area. 

'  The  very  considerable  fluctuations  from  day  to  day, 
especially  those  arising  from  unusual  and  unforeseen  occurrences, 
are  not  provided  for  entirely  by  even  very  large  and  well-arranged 
reservoirs.  To  provide  for  these  without  causing  shock,  the  rate 
of  filtration  must  be  changed  carefully  and  gradually,  and  the  first 
essential  to  success  is  a  good  regulation  apparatus." 

11  Responding  to  the  pumps  "  has  a  great  deal  to  recommend 
it.  It  allows  the  pure-water  reservoir  to  be  put  at  the  highest 
possible  level,  it  reduces  to  a  jninimum  the  loss  of  head  in  the 
plant,  and  yet  provides  automatically,  and  without  the  slightest 
trouble  on  the  part  of  the  attendants,  for  the  delivery  of  the 
required  quantity  of  water  by  the  filters  at  all  times.  If  the  filter 
are  connected  directly  to  the  pumps  there  is  a  tendency  for  the 
pulsations  of  the  pumps  to  disturb  their  operation,  which  is  highly 
objectionable,  even  if  the  pumps  are  far  removed;  and  this  exists 
where  filters  are  connected  directly  to  the  pumps,  and  a  pure- 
water  reservoir  is  attached  to  them  indirectly.  By  taking  all  the 
water  through  the  pure-water  reservoir  and  having  no  connection 
except  through  it,  this  condition  is  absolutely  avoided,  and  the 
pull  on  the  filters  is  at  all  times  perfectly  steady. 

Much  has  been  said  as  to  the  effect  of  variation  in  the  rate  of 
filtration  upon  the  efficiency  of  filters.  Experiments  have  been 
made  at  Lawrence  and  elsewhere  which  have  shown  that,  as  long 
as  the  maximum  rate  does  not  exceed  a  proper  one,  and  under 
reasonable  regulations,  and  with  the  filter  in  all  respects  in  good 


APPENDIX  XI.  313 

order,  no  marked  decrease  in  efficiency  results  from  moderate 
fluctuations  in  rate.  There  is  probably  a  greater  decrease  in 
efficiency  by  stopping  the  filter  altogether,  especially  if  it  is  done 
suddenly,  than  by  simply  reducing  the  rate.  The  former  some- 
times results  in  loosening  air-bubbles  in  the  sand,  which  rise  to 
the  surface  and  cause  disturbances,  but  this  is  not  often  caused  by 
simple  change  in  rate. 

On  the  whole,  there  is  little  evidence  to  show  that,  within 
reasonable  limits,  fluctuations  in  rate  are  objectionable,  or  should 
be  excluded  entirely,  especially  in  such  cases  as  at  Albany,  where 
arrangements  to  prevent  them  would  have  resulted  in  very  greatly 
increased  first  cost.  The  inferior  results  sometimes  obtained  with 
the  system  of  "  responding  to  the  pumps  "  as  it  existed  in  earlier 
works,  and  still  exists  in  many  important  places,  undoubtedly 
arises  from  the  fact  that  there  is  no  means  of  knowing  and  con- 
trolling the  simultaneous  rate  of  filtration  in  different  filters,  and 
that  one  filter  may  be  filtering  two  or  three  times  as  fast  as 
another,  with  nothing  to  indicate  it. 

This  contingency  is  fully  provided  for  in  the  Albany  plant. 
The  orifices  are  of  such  size  that  even  with  a  filter  just  scraped  and 
put  in  service,  with  the  minimum  loss  of  head,  with  the  outlet- 
gate  wide  open,  and  with  the  water-level  in  the  pure-water  reser- 
voir clear  d6wn — that  is,  with  the  most  unfavorable  conditions 
which  could  possibly  exist — the  rate  of  filtration  cannot  exceed 
5,000,000  or  6,000,000  gallons  per  acre  daily,  or  double  the 
nominal  rate.  This  rate,  while  much  too  high  for  a  filter  which 
has  just  been  cleaned,  is  not  nearly  as  high  as  was  possible,  and 
in  fact  actually  occurred  in  the  old  Stralau  filters  at  Berlin,  and  in 
many  English  works;  and,  further,  such  a  condition  could  only 
occur  through  the  gross  negligence  of  the  attendants,  because  the 
rate  of  filtration  is  indicated  clearly  at  all  times  by  the  gauges. 
These  regulating-devices  have  been  specially  designed  to  show  the 
rate  with  unmistakable  clearness,  so  that  no  attendant,  however 
stupid,  can  make  an  error  by  an  incorrect  computation  from  the 


FILTRATION  OF  PUBLIC    WATER-SUPPLIES. 

gauge  heights.  It  is  believed  that  the  advantage  of  clearness  by 
this  procedure  is  much  more  important  than  any  increased  accuracy 
which  might  be  secured  by  refinements  in  the  method  of  computa- 
tion, which  should  take  into  account  variations  in  the  value  of  the 
coefficient  of  discharge,  but  which  would  render  direct  readings 
impossible. 

In  designing  the  Albany  plant  the  object  has  been  to  combine 
the  best  features  of  German  regulation  with  the  economical  and 
convenient  features  of  the  older  English  system,  and  filters  are 
allowed  to  respond  to  the  pumps  within  certain  limits,  while 
guarding  against  the  dangers  ordinarily  incident  thereto. 

RESULTS    OF   OPERATION. 

The  filters  were  designed  to  remove  from  the  water  the 
bacteria  which  cause  disease.  They  have  already  reached  a 
bacterial  efficiency  of  over  99  per  cent,  and  it  is  expected  that 
their  use  will  result  in  a  great  reduction  in  the  death-rate  from 
water-borne  diseases  in  the  city.  They  also  remove  a  part  of  the 
color  and  all  of  the  suspended  matters  and  turbidity,  so  that  the 
water  is  satisfactory  in  its  physical  properties. 

The  filters  have  reached  with  perfect  ease  their  rated 
capacity,  and  on  several  occasions  have  been  operated  to  deliver 
one  third  more  than  this  amount;  that  is  to  say,  at  a  rate  of 
4,000,000  gallons  per  acre,  daily. 

COST    OF   CONSTRUCTION. 

The  approximate  cost  of  the  filtration-plant  complete  was  as 
follows : 

Land ' $8,290 

Pumping-station  and  intake 49,745 

Filters  and  sedimentation-basin,  with  piping 323,960 

Pure-water  conduit    and  connection  with   Quackenbush 

Street  pumping-station , 86,638 

Engineering  and  minor  expenses 28,000 


Total $496>633 


APPENDIX  XI.  315 

The  filters,  sedimentation-basin,  and  pure-water  reservoir  are 
connected  in  such  a  way  as  to  make  an  exact  separation  of  their 
costs  impossible;  but,  approximately,  the  sedimentation-basin 
cost  $60,000,  the  pure-water  reservoir  $9,000,  and  the  filters 
$255,000.  The  sedimentation-basin  thus  cost  $4,100  per  million 
gallons  capacity;  and  the  filters  complete  cost  $45,600  per  acre  of 
net  filtering  area,  including  all  piping,  office  and  laboratory  build- 
ing, but  exclusive  of  land  and  engineering. 

ACKNOWLEDGMENT. 

The  general  plan  and  location  of  the  plant  were  first  conceived 
by  the  Superintendent  of  Water-works,  George  I.  Bailey,  M.  Am. 
Soc.  C.  E.,  and  the  successful  execution  is  largely  due  to  his 
efforts.  The  members  of  the  Water  Board,  and  especially  the 
Construction  Committee,  have  followed  the  work  in  detail  closely 
and  personally,  and  their  interest  and  support  have  been  essential 
factors  in  the  results  accomplished.  In  the  designs  and  specifica- 
tions for  the  pure-water  conduit  the  author  is  greatly  indebted  to 
Emil  Kuichling,  M.  Am.  Soc.  C.  E.,  and  also  for  most  valuable 
suggestions  relative  to  the  performance  of  this  part  of  the  work. 
To  William  Wheeler,  M.  Am.  Soc.  C.  E.,  of  Boston,  the  author 
is  indebted  for  advice  upon  the  vaulting  and  cross-sections  of  the 
walls,  and  these  matters  were  submitted  to  him  before  the  plans 
were  put  in  final  shape.  All  the  architectural  designs  have  been 
supplied  by  Mr.  A.  W.  Fuller,  of  Albany.  W.  B.  Fuller, 
M.  Am.  Soc.  C.  E.,  as  Resident  Engineer,  has 'been  in  direct 
charge  of  the  work,  and  its  success  is  largely  due  to  his  interest  in 
it  and  the  close  attention  which  he  and  the  assistant  engineers 
have  given  it. 


INDEX. 


Albany,  N.  Y.,  filters  at,  254,  288. 

Alkalinity,    155. 

Altona,   double   filtration   at,    198. 

filters  at,  265. 
Alum,  use  of,  in  filtration,  92,  144. 
American  cities,  water-supplies  of,  and 

typhoid  fever  in,  211. 
Amsterdam,   filters  at,  272. 

iron  removal  at,   192. 
Anderson   process,    147. 
Antwerp,  filters  at,  272. 
Asbestos  as  filtering  material,  181. 
Asbury    Park,   iron   removal   at,    192. 
Ashland,   Wis.,   filters   at,   252. 
Area  of  filters  to  be  provided,  47. 

Bacteria,   apparent  and  actual   removal 
of,  by  filters,  87. 

from  underdrains,  87. 

in  Elbe  at  Altona,  228. 

in  faeces,  215. 

in  water,  84. 

number  to  be  allowed  in  filtered  wa- 
ter, 222. 

of  cholera  in  river  water,  231. 

of  typhoid  fever,  life^of,  in  water,  216. 

of  special  kinds  to  test  efficiency   of 
filtration,  86. 

to  be  determined  daily,  222. 
Bacterial   examination   of  water.  93. 
Berlin,  regulation  of  depth  of  water,  59. 

cholera  infantum  from  water,  229. 

friction    in   underdrains,   44. 

regulation  of  rate,  53,  55. 

water  works,  261. 
Berwyn,  Penn.,  filters  at,  253. 


Boston,   protection  of  purity  of  water- 
supply,  1 10. 

experimental  filters  at,  73. 
Bremen,  double  filtration  at,  198. 
Breslau,  filters  at,  274. 
Brussels,  ground-water,  supply  of,  276. 
Budapest,  filters  at,  274. 
Burton,    regulation    of    rate    at    Tokio, 
Japan,  58. 

Carpenter,  Prof.  L.  G.,  24. 

Chemnitz,  intermittent  filtration  at,  107. 

Chicago,    reduced   death-rate   with    new 

intake,   217. 
Cholera   infantum    from    impure   water, 

226. 
Cholera,  in  Hamburg  from  water,  230. 

caused  by  water,  214. 
Clarification,  definition  of,  113. 
Clark,  H.  W.,  24,  190. 
Clark's    process    for    softening    water, 

92,  145- 

Clay  particles,  size  of,  123. 
Cleaning  filters,  68. 
Coagulant,  absorption  of,  by  suspended 

matters,  154. 

successive  applications  of,  154. 
Coagulants  used  in  practice,  150. 
Coagulation  of  waters,  144. 
Cologne,    water-supply    of,    from    wells, 

276. 
Color,  113. 

amount  of  coagulant  required  to  re 

move,  153. 

amount  of,  in  various  waters,  115. 
measurement  of,  114. 

317 


INDEX. 


Color,  removal  of,  117. 
Continuous  filters,  5. 

filtration,  nature  of,  83,  92. 
Cost  of  filters  and  filtration,  4,  48,   102, 

200,  314. 

Covered  filters,  efficiency  of,   17. 
Covers  for  filters,  12,  15. 

at  Albany,  295. 

in  the  United  States,  17. 

omitted  at  Lawrence,   101. 
Crenothrix,  105,   186. 

Diarrhoea  from  impure  water,  226. 

Dibden,  W.  J.,  129. 

Disease  from  water,  210. 

Double  filtration  at  Schiedam,  273. 

Drainage  areas  of  a  number  of  rivers, 

-  133- 

Dresden,    water-supply    of,    from   filter- 
gallery,  276. 
Drown,  Dr.  Thomas  M.,  150,  191. 

Effective  size  of  sand,  21,  238. 

European   sands,  25. 
Efficiency  of  filtration,  83,  88,  91. 

effect  of  rate  upon,  50. 

effect  of  size  of  sand-grain  upon,  30. 

effect  of  thickness  of  sand  layer  upon, 

34- 

at  Lawrence,  106. 
European  filters,  91,  260. 
Effluents,  wasting  after  scraping,  74. 

Fseces,  number  of  bacteria  in,  215. 
Far  Rockaway,  L.  I.,  filters  at,  193,  253. 
Filling  sand  with  water  from  below,  68. 

307. 

Filter  beds,  bottoms  of,  must  be  water- 
tight, 12. 

covers  for,  12. 

form  of,  n. 

size  of,  10. 
Filters,   aggregate   capacity    of,   254. 

depths  of  waters  on,  45. 

list  of  cities  using,  244. 

reserve  area  required,  47. 

first  constructed  at  London,  83. 

for  household  use,  183. 

general  arrangement  of,  6. 


Filters,    statistics    of,    at   various    cities, 

241. 

Filtration,  cost  of,  200. 
degree  of  purification  required,  5. 
general  nature  of,  92. 
Fischer  tile  system,  181. 
FitzGerald,  Desmond,  73,  HI,  196. 
Flood  flows  not  taken  for  supply,  10. 
Frankel  and  Piefke,  experiments  on  re- 
moval of  disease  germs,  86. 
Frankfort   on    Main,    water    supply    of, 

from  springs,  276. 
Frankland,  Dr.  Percy,  84. 
Friction  of  filtered  water  in  pipes,  264. 
water  in  gravel,  37. 
water  in  sand,  22. 
water  in  underdrains,  40. 
Frost,  effect  of,  upon  filters,  12,  229,  266. 
Fruhling,   on  the   heating  of  water  by 

sunshine,  16. 

underdraining  at  Konigsburg,  39. 
Fuller,   G.   W.,   118,   123,   131,    139,   140, 
145,  152,  154,  161,  165. 

German  Imperial  Board  of  Health,  34, 

Si,  54,  75,  95- 

regulations  in  regard  to  filtration,  221. 
Gill,  apparatus  for  regulation,  55. 
Glasgow,    water-supply    of,    from    Loch 

Katrine,   275. 
Gravel  at  Albany,  299. 

layers,  35. 

friction  of  water  in,  37. 

screening  of,  for  filters,  37. 
Grand  Forks,  N.  D.,  filters  at,  252. 
Ground-water  supplies,  3. 

the  use  of,  in  Europe,  276. 

Halbertsma,  H.  P.  N.,  54,  59. 
Hamburg,     apparatus     for     regulating 
depth   of  water,   59. 

health  of,  226,  271. 

regulation  of  rate  of  filtration,  56. 

underdrains  of  filters  at,  42. 

water-supply  of,  269. 
Hamilton,  N.  Y.,  filters  at,  253. 
Hardness,  removal  of,  92,   145. 
Harrisburg,  Penn.,  filters  at,  253. 
Hermany,  Charles,  161. 


INDEX. 


319 


High  rates  of  filtration  without  coagu- 
lant, 182. 

Household  filters,   183. 
Hudson,  N.  Y.,  filters  at,  251. 

Ice  on  filters,   13. 
Inlet   regulators,   59. 
Impounding  reservoirs,  2. 
Intermittent  filtration,  97. 

application  of,  in,  197. 

at  Chemnitz,  107. 

at  Lawrence,  100. 

of  Pegan  Brook,  no. 
Iron,  compounds  of,  as  coagulants,  146. 

in  ground-waters,  186. 

in  ground-water  at  Lawrence,  105. 

metallic,  the  Anderson  process,  147. 

present  as  ferrous  sulphate,  191. 

removal  plants  in  operation,  192. 
Iron  waters,  treatment  of?  189. 

Jewel  filter,  151,  161,  162,  172,  173. 

Kirkwood,  James  P.,  8,  36,  47,  51,  55,  61, 

63,  67. 
Kiimmel,  50,  51,  86. 

Lambertsville,  N.  J.,  filters  at,  252. 
Lawrence  City  filter,  description  of,  100. 
Lawrence  Experiment  Station,  97. 
air  in  water  filtered  in  winter  at,  46. 
depth  of  sand  removed  at,  70. 
depth  of  water  on  filters,  46. 
effect  of  loss  of  head  upon  efficiency, 

61. 

effect  of  size  of  sand-grain  upon  effi- 
ciency, 32. 

effect  of  size  of  sand-grain  upon  fre- 
quency of  scraping,  32. 
efficiency  of  filters  at  various  rates,  50. 
efficiency  of  filtration  at,  86,  89. 
experiments    with    continuous    filtra- 
tion,  no. 

filters  of  fine  sand,  31. 
filters  of  various  sand-grain  sizes,  32. 
gravel  for  filters  at,  39. 
growth  of  bacteria  in  sterilized  sand 

at,  85. 
intermittent  filtration  investigated,  97. 


Lawrence   Experiment  Station,  method 
of  sand  analysis  at,  20. 

quantities  of  water  filtered  at  various 
losses  of  head,  66. 

wasting  effluents  not  necessary,  75. 
Lawrence,  typhoid  fever  at,  102. 
Leipzig,    water-supply    of,    from    wells, 

276. 
Lime  in  sand,  29. 

sterilizing  effect   of,    146. 

as  a  coagulant,  145. 

application  of,  to  water,   157. 
Lindley,  43,  51,  54,  57,  81. 
Literature  on  filtration,  277,  285. 
Little  Falls,  N.  Y.,  filters  at,  253. 
Loam  in  filters,  35. 

London,    cost    of    operating    filters    at, 
202. 

water-supply  of,  255. 
Long,  Prof.,  131. 

Lorain,  tests  of  mechanical  filters,  161. 
Loss  of  head,  52. 

limit  to,  60,  67. 

reasons  for  allowing  high,  65. 
Louisville,   mechanical  filters  at,   161. 

Magdeburg,  filters  at,  273. 
Maignen  system,   181. 
Manchester,   water-supply   of,   275. 
Manganese,    compounds    of,    as   coagu- 
lants, 148. 

in  ground-waters,  188. 
Massachusetts  State   Board   of   Health, 
see   Lawrence   Experiment  Station. 
Mechanical  filters,  159. 

application  of,  199. 

efficiency  of,  179. 

list  of,  247. 

pressure  filters.  180. 

rates  of  filtration  used,  175. 

types  of,  172. 

wasting  effluent  after  washing,  163. 
Millford.  Mass.,  filters  at,  252. 
Mills.  H.  F.,  97,  99,  102. 
Mount  Vernon,  N.  Y.,  filters  at,  252. 
Mud,   see  turbidity. 
Muddy  waters,  113. 

Munich,  water-supply  of,  from  springs, 
275- 


320 


INDEX. 


Nichols,    Prof.,    suspended    matters    in 

European   streams,    131. 
Nitrification,  effect  of,  upon  bacteria,  98. 

Odors,  removal  of,  by  filtration,  112. 
Organic  matters  in  water,  83. 
removed  by  intermittent  filters,  98. 

Paper  manufacturing,  filtration  of  wa- 
ter for,  5. 

Paris,   ground-water  supply  of,  276. 

Palmer,  Prof.,  131. 

Passages  through  the  sand  in  filters,  67. 

Pegan  Brook,  purification  of,   no. 

Period,  how  computed  and  length  of,  72. 
length  of,  dependent  upon  turbidity, 
137- 

Piefke,  48,  50,  54,  63,  69,  73,  74,  75,  80, 
84,  85,  90. 

Pittsburgh,  experiments  with  mechan- 
ical filters,  162. 

Plagge  and  Proskower,  84. 

Plymouth,  Penn.,  typhoid  fever  at,  208. 

.Pollution    of    European    water-supplres, 

93- 

Polluted  waters,  utilization  of  excessive- 
ly, in. 

Porcelain  filters  for  household  use,  183. 
Poughkeepsie,  N.  Y.,  filters  at,  251. 
Pressure  filters,  180. 
Providence,  mechanical  filters  »at,   159. 

Rate  of  filtration,  47,  224. 

at  various  places,  241. 

effect  of,  upon  cost,  48. 

effect  of,  upon  efficiency,  50. 

lower  after  scraping,  76. 

regulation  of,  52. 

Red  Bank,  N.  J.,  filters  at,  193,  253. 
Regulation  of  filters,  52. 

old  forms  of  regulators,  52. 

modern  forms  of  regulators,  54. 

at  Albany,  305,  308,  310. 

of  mechanical  filters,  178. 
Reincke,  Dr.,  report  on  health  of  Ham- 
burg for  1892,  226. 
Reinsch  on  the  cause  of  poor  filtration 

at  Altona,  267. 
Reserve  area  required  in  case  of  ice,  18. 


Reservoirs,  purposes  served  by,  133. 
Rock  Island,  111.,  filters  at,  254. 
Roofs  for  filters,  16. 
Rotterdam,  filters  at,  272. 

St.  Johnsbury,  Vt.,  filters  at,  251. 

St.   Louis,   regulators   for  proposed  fi 

ters,  55. 

St.  Petersburg,  filters  at,  275. 
Samuelson,  51. 
Sand,  20. 

at  Albany,  301. 

analysis  of  European,  25. 

analysis  of,  from  leading  works,  28. 

appliances  for  moving,  68. 

compactness  of,  in  natural  banks,  6 

depth  of,  in  filters,  34. 

depth  to  be  removed  from  filters,  6 

dune,  26. 

dune,  washing  of,  impossible,  82. 

effect  of  grain-size  upon  frequency  < 
scraping,  32. 

effect  of  grain-size  upon  the  erficienc 
30. 

effective  size  of,  21,  238. 

extra  scraping  before  replacing  fres 

71. 

for  filtration,  20,  33. 
for  mechanical  filters,  175. 
friction  of  water  in,  22. 
grain-size  of,  20,  233. 
in  European  filters,  24. 
in  Lawrence  filters,  two  sizes  of,  10 
lime  in,  29. 

method  of  analysis  of,  233. 
quantity  to  be  removed  by  scrapin 

74- 

replacing,  71. 

selection  of,  33. 

size  of  passages  between  grains  of, 

sterilized,  experiments  with,  85. 

thickness  of  layer,  34. 

uniformity  coefficient,  21,  238. 
Sand  washing,  26,  76,  304. 

cost  of,  81. 

water  for,  80. 

Sandstone  filters  for  household  use,  i£ 
Schiedam,  double  filtration  at,  273. 
Scraping  filters,  7,  68. 


INDEX. 


321 


Scraping    filters,    amount    of    labor    re- 
quired for,  81. 

depth  of  sand  removed,  33,  66,  69. 

frequency  of.  49.  ~2.  241. 
Sedgwick,  Prof.  \Y.  T..  86. 
Sediment,  removal  of,  92,  133. 
Sediment  layer,  6,  31. 

influence   of,   upon   bacterial   purifica- 
tion, 84. 

thickness  of,  33,  66,  69. 
Sedimentation  basins,  8,  133,  293. 

effect  of,   134. 

Sewage,  number  of  bacteria  in,  215. 
Simpson,  James,  83. 
Soda-ash,   application   of,    157. 
Somersworth,  X.  H.,  filters  at,  253. 
Storage  for  raw  water,  136. 
Subsidence,  limits  to  the  use  of,  142. 
Sulphate    of   alumina,    action    of.    upon 

waters,  144. 

Surface-waters,  use  of,  unfiltered,  275. 
Suspended  matters,   113,   117. 

in  relation  to  turbidities,  122. 

in  various  waters,  129. 

The  Hague,  iron  removal  at,  192. 
Tokio,  regulation  of  rate  at,  58. 
Trenched  bottoms  for  filters,  36,  40,  100. 
Turbidity,  92,   113. 

amount  which  is  noticeable.  121. 

amount  in  several  streams,  124. 

duration  of,  128. 

in  relation  to  suspended  matters,  122. 

measurement  of,    117. 

power  of  sand  filters  to  remove,  139. 

preliminary  processes  to  remove,  133. 

source  of,  123. 

Typhoid  fever  in  Berlin  and  Altona,  12, 
85,  267. 

in  American  cities,  211. 


Typhoid  fever  in   Hamburg,  271. 

in  Lawrence,  102. 

in  London,  259. 

in  Zurich.  275. 

Typhoid-fever  germs,  life  of,  in  water. 
216. 

Underdrains,  35,  39. 

bacteria  from,  87. 

friction  of,  at  Albany,  299. 

size  of,  41. 

ventilators  for,  44. 
Uniformity  coefficient  of  sand.  21,  238. 

Ventilators  for  underdrains,  44. 
Vienna,  water-supply  of,  from  springs, 
276. 

Warren  filter,  151,  161,  162.  172.  176,  177. 
Warsaw,  filters  at,  275. 

friction  in  underdrains,  43. 

regulation  of  rate  at,  57. 
Wasting  effluents,  74. 
Water,  depth  of,  on  filters,  45.  59. 

heating  of,  in  filters,  45. 

organic  matters  in,  83. 
Water-supplies  of  American  cities,  211. 
Water-supply  and  disease,  210. 
Waters,  what  require  filtration,  207. 
Weston,  E.  B.,  153,  154,  159. 
Weston,  R.  S.,  153,  189. 
West  Superior,  iron  in  ground-water  at, 

189. 
Winter,  effect  of,  upon  filtration,  12. 

temperatures    of   places   having   open 

and  covered  filters,   15. 
Worms  tile  system,  181. 

Zurich,  filters  at,  274, 


•T 


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JUN          193? 


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